2018

Grain growth is a ubiquitous phenomenon in all materials, and it affects both structural and functional properties. Despite its intrinsic importance, a full comprehension of grain growth from a fundamental point of view-i.e., from the nanoscale to the macroscale-is still a pending issue. In practical terms, our knowledge relies on the classical kinetic laws reported sixty years ago.

This paper reports the violation of such classical laws in boron carbide ceramics consolidated by spark plasma sintering. The conjunction of high temperature gradients with large compressive stress when a pulse electric current passes through the ceramic powders gives rise to an intense twinning-detwinning formation. These forming steps at the grain boundaries change the grain mobility drastically. Therefore, a new 'exotic' law for grain-growth kinetics is found and validated at different temperatures and dwell times.

The present paper demonstrates an easy and scalable mechanochemical synthesis of ternary sulfide Cu2SnS3 (CTS) as a promising solar cell absorber. For the synthesis, pre-milled nanoparticles of CuS and SnS were used. The pure CTS phase was readily obtained after 60 min of milling in a laboratory planetary ball mill and 240 min in an industrial eccentric vibration industrial mill, respectively. The reaction progress of laboratory scale synthesis was studied by the quantitative Rietveld analysis. The reaction speed reaches its maximum at 4.6 min and the reaction is completed at approximately 60 min, according to the fitted data. The products of the syntheses were further characterized by X-ray powder diffractometry, Raman spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and UV-Vis spectroscopy. The results revealed formation of near-stoichiometric CTS nanoparticles with tetragonal I-42m symmetry. An average crystallites size of approximately 10-15 nm was determined for CTS phase. The SEM images support quintessential polydisperse character of the powders obtained by ball-milling approach. The materials seem to be suitable for photovoltaic applications with the band-gap energies of approximately 1.16-1.19 eV.

Niobium carbonitride [Nb(C,N)] nanoparticles were synthesized by a combustive mechanochemical reaction in the Mg/Nb2O5/C3H6N6 system. High-energy ball milling was used to promote a mechanically induced self-sustaining reaction (MSR). Combustion occurred after a very short milling period of 5 min. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS) analyses revealed that the nature of the product is an intermixed carbonitride material. The formation mechanism of Nb(C,N) resulted from the magnesiothermic reduction of niobium oxide to generate elemental Nb, which then reacted with the species generated from the melamine decomposition.

Optimizing the homogenization technique for graphene nanoplatelet/yttria tetragonal zirconia composites: Influence on the microstructure and the electrical conductivity

3 mol% yttria tetragonal zirconia polycrystalline (3YTZP) ceramic composite powders with 10 vol% nominal content of graphene nanoplatelets (GNPs) were prepared using four different homogenization routines: dispersion of the powder mixture by ultrasonication in isopropyl alcohol, homogenization in a high-energy planetary ball mill in wet or dry conditions after ultrasonication, and milling of the powders in a high-energy planetary ball mill in dry conditions. A significant effect of the homogenization routine on the powders particle size distribution was revealed by laser granulometry and Raman spectroscopy. Highly densified composites were obtained after spark plasma sintering (SPS) and remarkable differences on the GNP size, shape and distribution throughout the ceramic matrix and also in the electrical conductivity were observed in the four different composites. The composite with the best performance in terms of electrical conductivity was the one prepared after planetary ball milling of the powders in dry conditions as a consequence of the reduced dimensions of the GNPs and their excellent distribution throughout the ceramic matrix.

The role of carbon nanotubes on the stability of tetragonal zirconia polycrystals

The effect of single walled carbon nanotubes (SWNT) at zirconia grain boundaries on the stability of a tetragonal zirconia polycrystalline matrix has been explored in as-sintered composites and after low temperature hydro thermal degradation (LTD) experiments. For this purpose, highly-dense 3 mol% Y2O3-doped tetragonal zirconia polycrystalline (3YTZP) ceramics and SWNT/3YTZP composites were prepared by spark plasma sintering (SPS). Quantitative X-ray diffraction analysis and microstructural observations point out that an increasing amount of well-dispersed SWNT bundles surrounding zirconia grains decreases the metastable tetragonal phase retention in the ceramic matrix after sintering. In contrast, the tetragonal ceramic grains in composites with SWNTs are less sensitive to the presence of water, i.e. to undergo a martensitic transformation under LTD conditions, than monolithic 3YTZP ceramics. The SWNT incorporation diminishes micro-cracking due to tetragonal to monoclinic ZrO2 phase transformation in the composites.

The sintering of fine-grained a-alumina by spark plasma sintering (SPS) was performed to study grain growth under SPS conditions. Grain growth is found to be extensive at relative densities above 95%. A grain growth versus dwell time analysis during SPS allows for the determination of the grain-boundary diffusion coefficient. This study shows that the remarkable enhancement of grain-boundary diffusion derived from a previous analysis could be a consequence of the presence of the recently discovered "disconnections" at the grain boundaries of alpha-alumina. Their presence, together with their electric charge and the external electric field at the boundaries, are the key ingredients for a violation of the typical grain growth kinetic law. When they are introduced appropriately, an updated value of the grain-boundary diffusion coefficient is achieved. A comparison with other values reported previously in the literature through other techniques and a critical analysis are also carried out.

Biomass fly ash and aluminium industry slags-based geopolymers

Geopolymers are a new class of non-Portland cements produced using an alumino-silicate material and an activating solution, which is mainly composed of sodium or potassium and waterglass to be subsequently cured at relatively low temperatures. Those can be formulated by adding natural minerals, waste and/or industrial by-products. The study investigates the microstructural properties of geopolymers synthesized from metakaolin (MK) and the admixture of fly ash (FBA) and aluminium industry slags (AIS) at different ages of curing. Five different geopolymer compositions were prepared and characterized by XRD, ATR-FTIR and SEM/EDS. The study revealed that geopolymeric gels are identified, which show mainly glassy microstructures, in agreement with the X-ray amorphous diffraction patterns, broad FTIR features and confirmed by SEM/EDS, with promising results prior to an industrial scale.

Fly ash is a biomass combustion by-product produced by dragging ash from the base of the furnace. Disposing of ash is a growing economic and environmental burden. Based on physical and chemical properties, fly ash could be used in the manufacture of construction materials. This paper investigates the influence of biomass fly ash from olive pomace as additive to manufacture of clay ceramic composite materials. Fired clay brick at 950 degrees C were prepared containing between 0 and 25 wt% fly ash. Final products are studied by water absorption, bulk density, loss of ignition, linear shrinkage, compressive strength and physisorption N-2. The results reveal that the porosity of the materials increases with the level of fly ash replacement (10% up to 25 wt%) resulting in to increased water absorption and decreased compressive strength. Fired clay brick developed in this study can be used for construction materials based on criteria of the current regulations.

Study of the thermal decomposition of historical metal threads

In this work, it is reported that thermal analysis techniques such as differential thermal analysis and thermogravimetric analysis are very useful for evaluating metals threads and fibres used in the manufacture of historical artifacts. Thermal analysis has been used to characterize the silk, cotton and linen employed as supports and the copper, silver and aluminium as the metallic components in the studied threads. Other organic compounds, mainly added for the conservation of the threads, have also been characterized.

A direct in situ observation of water-enhanced proton conductivity of Eu-doped ZrO2: Effect on WGS reaction

Eu-doped ZrO2 solid solutions have been synthesized in order to prepare proton conductors as water-enhancer additives for the WGS reaction. Elemental characterization has been carried out revealing homogeneous dopant distribution resulting in fluorite-type solid solutions for Eu2O3 contents up to similar to 9 mol.%. Representative samples of the Eu-doped ZrO2 series have been analysed by Impedance Spectroscopy (IS) in inert, oxygen and wet conditions. The solid solution with 5 mol.% of Eu2O3 has presented the highest conductivity values for all tested conditions indicating an optimal amount of dopant. Moreover, the presence of vapour pressure results in an increment of the conductivity at temperatures lower than 300 degrees C, meanwhile at higher temperatures the conductivity is the same than that in inert conditions. To elucidate these results, in situ DRIFTS studies were carried out. These experiments evidenced the existence of water dissociation at oxygen vacancies (band at 3724 cm(-1)) as well as the presence of physisorbed water at temperatures up to similar to 300 degrees C where the band at 5248 cm(-1) characteristic of these species disappeared. These results points to a layer model where the physisorbed water interacts with surface hydroxyls generated by dissociated water that improves the proton conductivity through Grotthuss' mechanism in the RT-300 degrees C temperature range. These samples were successfully tested in WGS reaction as additive to a typical Pt-based catalyst. The presence of the mixed oxide reveals an increase of the catalyst' activity assisted by the proton conductor, since improves the water activation step.

Graphene or carbon nanofiber-reinforced zirconia composites: Are they really worthwhile for structural applications?

The use of allotropic phases of carbon (i.e. nanotubes, graphene or carbon nanofibers) as second phases to design ceramic composites is a hot topic at present. Researchers try to provide a remarkable improvement of the parent ceramic assuming that some of the outstanding mechanical properties of these phases migrate to the resultant composite. This reasonable idea has been questioned severely in the case of nanotubes addition but there is not any analysis for the other two phases cited previously. To elucidate this question, zirconia was selected as a model ceramic. This paper reports the mechanical properties of zirconia composites reinforced either with graphene or carbon nanofibers, with special emphasis on the high-temperature plasticity.

Mechanosynthesis of Sr1-xLaxTiO3 anodes for SOFCs: Structure and electrical conductivity

Sr1-xLaxTiO3 (SLT; 0 <= x <= 0.5) powder samples were synthesised at room temperature by a mechanochemical method from SrO, La2O3 and TiO2 mixtures in 90 min. The obtained SLT samples as potential anode materials in solid oxide fuel cells (SOFCs) were investigated. The microstructure, electrical conductivity and chemical compatibility with yttria-stabilised zirconia (YSZ) were studied. The powder samples had a nanometric character after milling. After a subsequently heating at 900 degrees C, the particle size slightly increased, but still remained nanometric. At this high temperature, a good chemical compatibility with YSZ was found. The x = 0.2 sample gave the best electrical conductivity values, i.e. 0.23 W cm(-2). These features make such as-obtained samples good candidates to be used as anodes in SOFCs.

Vanadium carbonitride (VCN) nanoparticles were synthesized by a mechanically induced magnesiothermic combustion in a Mg/V2O5/C3H6N6 system. Initial materials ignited after a short milling time of 6 min. Various characterizations such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDX), high-resolution transmission electron microscopy (HRTEM) and elemental mapping confirmed that the product of the combustion was a mixed carbonitride. In this process, magnesium reduces vanadium oxide to generate elemental V and a great amount of heat. Melamine decomposes due to the temperature rise, and its decomposed species form the carbonitride compound. The chemical composition of the synthesized product was estimated to be VC0.26N0.36.

In this work, we studied the thermal decomposition of a widely employed silicone elastomer, polydimethylsiloxane, in an inert atmosphere. This silicone elastomer has several applications due to its high thermal stability such as MEMS (microelectromechanical systems) precursors, microfluidic components, adhesives, lubricants, and precursors for non-porous ceramics. Therefore, a reliable description of the thermal decomposition kinetics is important to prevent or control the decomposition in such applications. While the decomposition has been amply reported as a complex process, most kinetic studies published on this system use simplified methods that avoid the fact that the entire process cannot be described by a single kinetic triplet. Here, we have studied the decomposition process by first separating the overall reaction into its three constituent steps which were subsequently analysed independently. The deconvolution was carried out using Fraser-Suzuki function that is capable of fitting an asymmetric peak fitting function. The resulting kinetic parameters proved to be able to reconstruct the original experimental curves but are also capable of producing accurate predictions of curves recorded at heating schedules different from those employed to record the experimental data used in the kinetic analysis. Finally, it was found that the rate limiting step of all stages is the diffusion of the gases released during the polymer decomposition through the transforming polymeric matrix.

An approach to the heating dynamics of residues from greenhouse-crop plant biomass originated by tomatoes (Solanum lycopersicum, L.)

The most representative of greenhouse-crop plant biomass residues of tomatoes (Solanum lycopersicum L.) were selected for this study by using X-ray fluorescence spectrometry (XRF) and X-ray powder diffraction (XRD). The heating dynamics in air in the 600-1150 degrees C range of these residues for the production of renewable energy and the resultant ashes have been investigated. A total of 11 elements were determined by XRF in the biomass ashes and some minor elements. The content of alkaline elements and chlorides decreased as increasing heating temperature and disappeared at 1150 degrees C. Alkaline salts, NaCl and KCl, were volatilized by heating since 800 degrees C. The total contents of S and P in the biomass ashes were associated to CaSO4, and a complex phosphate identified by XRD. CaCO3 present at 600 degrees C was decomposed to CaO with disappearance at 1000 degrees C. By heating, new silicates were formed by solid-state reactions in the biomass residue. The minor elements have been found in a relative proportion lower than 0.9wt.% and they characterized the obtained ashes, with potential use as micronutrients.

The waste vitrification of abandoned open sky vermiculite deposits has been considered by combining with a natural phosphate mineral residue. Several batches haven been designed from the composition system: Li2O-MgO-Al2O3-P2O5-SiO2 including some Fe2O3 and Fluoride. The resulting glasses are transparent and smooth green coloured, giving rise after TTT treatments to several opal, opaque glass-ceramics with iridescent surface. Full characterization has been carried out by XRD and electron microscopy with EDS, as well as by XPS spectroscopies, concluding that the main crystalline phases formed were alpha-cordierite and beta-spodumene. The surface of these glass-ceramics from vermiculiteamblygonite is enriched in Fe2O3. Compared to the parent glasses, the final glass-ceramics exhibited and improvement in fracture toughness.

Here, a kinetic study of the thermal decomposition of synthesized hydrotalcite, Mg-6 Al-2 CO3(OH)(16)center dot H2O, has been carried out using thermogravimetric experiments in air atmosphere. It is shown that the thermal decomposition occurs in two well differentiated stages. The first one is a single-step dehydration process that comprises the release of four water molecules. On the other hand, the second stage is complex and corresponds to both dehydroxylation and decarbonation processes which occur simultaneously. The kinetic parameters describing all processes were calculated by means of a combined approach comprising isoconversional, model-fitting and deconvolution methods. It was concluded that dehydroxilation and decarbonization cannot be separated by TG experiments and the two stages contributing to the complex process do not apparently match the expected stoichiometry of the process. Therefore, it is proposed that such stages mark a change on the reaction mechanism due to the structural collapse of the laminar double hydroxide.

Synergy achieved in silver-TiO2 nanocomposites for the inhibition of biofouling on limestone

Biodeterioration of stone monuments is estimated to be as high as 20-30% of the total degradation suffered by Cultural Heritage constructions. With regard to this problem, bactericidal treatments are mainly based on cleaning. These processes, while effective in the short term, require frequent reapplications increasing potential damages to the monument. Silver nanoparticles offer many advantages over traditionally employed products, such as their prolonged biocide efficacy and their low toxicity to humans and environment. The aim of this study was to evaluate the applicability and effectiveness of seven nanocomposite treatments based on titanium dioxide and/or silver nanoparticles to prevent biodeterioration of limestone monuments. These nanocomposites were characterized by UV Visible spectrophotometry, Dynamic Light Scattering and Electron Microscopy. To assess their bactericidal activity, accelerated weathering tests were performed on limestones from the quarry of Utrera, a source widely employed in such iconic monuments as the Cathedral of Seville (Spain). Furthermore, the samples of biopatina employed in our assays stemmed from the fa ades of historical buildings from Seville. Our results show that silver and titanium dioxide nanocomposites stabilized by citrate achieve a high biocide effect while maintaining color alterations at a low level.

On the determination of thermal degradation effects and detection techniques for thermoplastic composites obtained by automatic lamination

Automatic lay-up and in-situ consolidation with thermoplastic composite materials is a technology under research for its expected use in the profitable manufacturing of structural aeronautical parts. This study is devoted to analysing the possible effects of thermal degradation produced by this manufacturing technique.
Rheological measurements showed that there is negligible degradation in PEEK for the temperatures reached during the process. Thermogravimetric analysis under linear heating and constant rate conditions show that thermal degradation is a complex process with a number of overlapping steps. A general kinetic equation that describes the degradation of the material with temperature has been proposed and validated. Attenuated total reflectance Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy confirmed that there is no remarkable degradation. The use of a combination of in-situ and ex-situ experimental techniques, including kinetic modelling, not only provides reliable information about degradation but also allows setting optimal processing conditions.

Synthesis and characterization of SiC/Si3N4 composites from rice husks

SiC-Si3N4 composites have been obtained by carbothermal reduction of rice husk under a nitrogen-argon atmosphere at 1450 degrees C, which is a lower temperature than those used by other authors. On the other hand, tailoring the argon/nitrogen ratio led to the obtained of SiC-Si3N4 composites across the whole range of compositions. Phosphoric acid treatment permited the synthesis of the composite without a pyrolysis step. The final products were characterized by X-ray diffractometry, IR spectroscopy and scanning electron microscopy.

The rapid mechanochemical synthesis of nanocrystalline CuFeS2 particles prepared by high-energy milling for 60 min in a planetary mill from copper, iron and sulphur elements is reported. The CuFeS2 nanoparticles crystallize in tetragonal structure with mean crystallite size of about 38 ± 1 nm determined by XRD analysis. HRTEM study also revealed the presence of nanocrystals with the size of 5–30 nm with the tendency to form agglomerates. The Raman spectrum confirms the chalcopyrite structure. Low temperature magnetic data for CuFeS2 support the coexistence of antiferromagnetic and paramagnetic spin structure. Moreover, the hysteresis loops taken at temperatures from 5 K to 300 K revealed a presence of very small amount of ferromagnetic phase, which seems to be associated with the non-consumed elemental Fe in as-prepared nanoparticles. The optical band gap of CuFeS2nanoparticles has been detected to be 1.05 eV, larger than band gap of the bulk material. The wider gap possibly resulted from the nano-size effect. Photoresponses of CuFeS2nanoparticles were confirmed by I-V measurements under dark and light illumination. It was demonstrated that mechanochemical synthesis can be successfully employed in the one step preparation of nanocrystalline CuFeS2 with good structural, magnetic, optical and electrooptical properties.

The effect of vitreous phase on mullite and mullite-based ceramic composites from kaolin wastes as by-products of mining, sericite clays and kaolinite

Mullite precursors were prepared using kaolin waste, sericite clay containing kaolinite and industrial kaolin with addition of alumina in a wet medium to synthesize mullite (72 wt% Al2O3 and 28 wt% SiO2). Uniaxial pressed bars of the powdered mullite precursors were fired in the range 1400-1600 degrees C with soaking times 30-120 min. The resultant materials were studied by XRD and SEM-EDX. Bulk densities, apparent porosities and flexural strengths in four points were determined in the fired bars at 1500, 1550 and 1600 degrees C. It was concluded that the thermal behaviour of these mullite precursors was influenced by the presence of impurities in the raw materials. These impurities originate a liquid phase forming a glassy phase which produces a progressive and enhanced densification of the mullite materials by reaction sintering at 1500-1600 degrees C. The technical properties were also influenced by the relative proportion of vitreous phase. The microstructure of characteristic mullite crystals was revealed by SEM. It was emphasized the use of kaolin waste by-products of mining and sericite clays as valuable raw materials for mullite preparation.

Pressure Effect on the Multicycle Activity of Natural Carbonates and a Ca/Zr Composite for Energy Storage of Concentrated Solar Power

This work is focused on the use of the Calcium-Looping process (CaL) in Concentrated Solar Power (CSP) plants for Thermochemical Energy Storage (TCES). Cheap, abundant and nontoxic natural carbonate minerals, such as limestone and dolomite, can be employed in this application to store energy through the cyclic calcination/carbonation of CaCO3. In a recent work, a closed CO2 cycle has been proposed for an efficient CaL-CSP integration in which the CO2 in excess effluent from the carbonator is used to generate electricity by means of a gas turbine. Process simulations show that the thermoelectric efficiency is enhanced as the carbonator pressure and temperature are increased provided that the multicycle CaO conversion is not affected. On the other hand, the use of just one reactor for both calcination and carbonation has been suggested to reduce capital cost. However, the experimental results shown in the present work indicate that sintering is notably enhanced as the pressure in the reactor is increased. Such an adverse effect is mitigated for a ZrO2/CaCO3 composite with a low Zr content as compared to natural carbonates. These results are relevant to process simulations for better assessing the global efficiency of the CaL-CSP integration.

Effects of milling time, sintering temperature, Al content on the chemical nature, microhardness and microstructure of mechanochemically synthesized FeCoNiCrMn high entropy alloy

FeCoNiCrMn(Al)-based powdered high entropy alloys were synthesized by a short time mechanical alloying process in a high energy planetary ball milling from mixtures of elemental powders, and subsequently sintered by a pressureless procedure. The composition and microstructure of the HEA phases before and after the sintering process were studied by X-ray diffraction, energy dispersive X-ray analysis (EDX) and scanning electron microscopy. The microhardness and tensile strength values for Fe1,8Co1,8Ni1,8Cr1,8Mn1,8Al1,0 HEA sintered at 1400 degrees C sample were 3,7 GPa and 1011 MPa, respectively. Statistical Fisher-Pearson coefficient of skewness and kurtosis were played to determine the optimum synthesis milling time. The use of NaCl as additive led on to a reduction of the as-milled grain size. After sintering, SEM study confirmed a segregation of the initial HEA phase directly related to the melting temperature of the elements. Three melting temperature groups were described (Cr, FeCoNi and Mn) and they agree with the observation in the elemental mapping study. The presence of Al favored the segregation of Cr.

Thermochemical energy storage (TCES) is considered as a promising technology to accomplish high energy storage efficiency in concentrating solar power (CSP) plants. Among the various possibilities, the calcium-looping (CaL) process, based on the reversible calcination–carbonation of CaCO3 stands as a main candidate due to the high energy density achievable and the extremely low price, nontoxicity, and wide availability of natural CaO precursors such as limestone. The CaL process is already widely studied for CO2 capture in fossil fuel power plants or to enhance H2 production from methane reforming. Either one of these applications requires particular reaction conditions to which the sorbent performance (reaction kinetics and multicycle conversion) is extremely sensitive. Therefore, specific models based on the conditions of any particular application are needed. To get a grip on the optimum conditions for the carbonation of limestone derived CaO in the CaL-CSP integration, in the present work is pursued a multidisciplinary approach that combines theoretical modeling on reaction kinetics, lab-scale experimental tests at relevant CaL conditions for TCES, process modeling, and simulations. A new analytic equation to estimate the carbonation reaction rate as a function of CO2 partial pressure and temperature is proposed and validated with experimental data. Using the kinetics analysis, a carbonator model is proposed to assess the average carbonation degree of the solids. After that, the carbonator model is incorporated into an overall process integration scheme to address the optimum operation conditions from thermodynamic and kinetics considerations. Results from process simulations show that the highest efficiencies for the CaL-CSP integration are achieved at carbonator absolute pressures of ∼3.5–4 bar, which leads to an overall plant efficiency (net electric power to net solar thermal power) around 41% when carbonation is carried out at 950 °C under pure CO2

Crystallization is one key aspect in the resulting properties of nanocrystalline functional materials, and much effort has been devoted to understanding the physical mechanisms involved in these processes as a function of temperature. The main problems associated with crystallization kinetic studies come from the limitations of the employed techniques, and the obtained results may vary significantly depending on the choice of the measurement method. In this work, a complete description of the thermal crystallization event of nanocrystalline BiFeO3 has been performed by combining the information obtained from three different experimental techniques: in situ high-temperature X-ray diffraction, transmission electron microscopy, and differential scanning calorimetry. Interestingly, the kinetic analysis of the X-ray diffraction and differential scanning calorimetry data yields almost identical results, although the physical properties measured by both techniques are different. This allows the unambiguous determination of the kinetic parameters. The importance of a proper definition of the conversion degree, which is limited by the employed measurement technique, is also highlighted.

A novel fine-grained orthorhombic ZrO2 ceramic stabilized with 12 mol% Ta doping was fabricated by spark plasma sintering from home-made powders, and its high-temperature mechanical properties evaluated for the first time by compressive creep tests in both Ar and air. It was found that the high-temperature plasticity of the ceramic deformed in Ar, under which the Ta-doped orthorhombic ZrO2 is a black suboxide with abundant oxygen vacancies in its crystal structure, is controlled by grain boundary sliding (stress exponent similar to 2, and activation energy similar to 780-800 kJ/mol). However, the high-temperature plasticity of the ceramic deformed in air, under which the Ta-doped orthorhombic ZrO2 is a white oxide due to the elimination in situ of oxygen vacancies, is controlled by recovery creep (stress exponent 3, and activation energy similar to 750 kJ/mol). It was also observed that black Ta-doped orthorhombic ZrO2 is more creep resistant than its white counterpart with the same grain size, and that the former deforms as the more conventional Y2O3-stabilized ZrO2 does.

Fabrication and characterization of WC-HEA cemented carbide based on the CoCrFeNiMn high entropy alloy

A high entropy alloy (HEA, CoCrFeNiMn) synthesized by mechanical alloying was used as the binder for the densification of WC by a pressureless high temperature procedure. Three different WC were used by modifying its microstructure with a high energy ball milling treatment. The alloy content in the HEA-WC mixture was varied from 10 to 30% vol. The microstructure and properties of the sintered composites were studied by X-ray diffraction, scanning electron microscopy and microindentation.

Influence of the Mn content on the TiNbxMn alloys with a novel fcc structure

This work studies the structural evolution of TiNbxMn alloys (x: 0-12 wt%) synthetized by mechanical alloying in a planetary ball mill with different milling times between 1 h and 120 h. The specimens were characterized by X-ray diffraction patterns, scanning and transmission electron microscopies and Energy-dispersive X-ray spectroscopy. It was observed an evolution of the alloys developed from the raw Ti, Nb and Mn elements to bcc-TiNbxMn alloys and, finally, novel fcc-TiNbxMn alloys, with Fm3m space group symmetry, not previously observed. The presence of Mn promotes other interesting effects: a) the decreasing of the crystallite and the particle sizes, reaching values close to 4 nm and 400 nm, respectively, b) the partial amorphization of the fcc-TiNbxMn alloys due to the combined effect of the Mechanical Alloying and the difference of Mn atomic size in comparison with Ti and Nb and c) the presence of Mn that decreases the Fe amount (from milling media) in the as-milled powders.

Effects of additives on the synthesis of TiCxN1-x by a solid-gas mechanically induced self-sustaining reaction

The synthesis of TiCxN1-x from Ti/C mixtures in a N-2 atmosphere performed in a high-energy planetary mill was used as example to study the influence of the use of additives in mechanically induced self-sustaining reaction (MSR) processes. In particular, the effect of the addition of TiN, TiC, Si3N4 and SiC was analyzed. The self-sustaining reaction was extinguished when additive contents of 50, 40, 40 and 30 wt% for TiN, TiC, Si3N4 and SiC, respectively, were employed. These additives cannot be regarded as real inert since they served as an extra solid source for nitrogen and carbon, modifying the final stoichiometry of the TiCxN1-x phase. The adiabatic temperature (T-ad) determined for the mixtures with no MSR effect was well above the empirical limit value of 1800 K adopted as criterion for the occurrence of the self-propagating high-temperature synthesis (SHS) process. The ignition time (t(ig)) of the MSR process was practically invariant for low additive contents (approximately 50 min) and tended to increase up to maximum values of 85-95 min for the larger additive contents.

Thermal behaviour of sericite clays as precursors of mullite materials

Thermal analysis of some sericite clays, from several deposits in Spain, which are not exploited at this time, has been studied. The samples have been previously characterized by mineralogical and chemical analysis. Sericite clays have interesting properties, with implications in ceramics and advanced materials, in particular concerning the formation of mullite by heating. According to this investigation by differential thermal and thermogravimetric analysis (DTA-TG), the sericite clay samples can be classified as: Group (I), sericite-kaolinite clays, with high or medium sericite content, characterized by an endothermic DTA peak of dehydroxylation of kaolinite with mass loss, which overlapped with dehydroxylation of sericite, and Group (II), sericite-kaolinite-pyrophyllite clays, with broader endothermic DTA peaks, in which kaolinite is dehydroxylated first and later sericite and pyrophyllite with the main mass loss, appearing the peaks overlapped. X-ray diffraction analysis of the heated sericite clay samples evidenced the decomposition of dehydroxylated sericite and its disappearance at 1050 A degrees C, with formation of mullite, the progressive disappearance of quartz and the formation of amorphous glassy phase. The vitrification temperature is similar to 1250 A degrees C in all these samples, with slight variations in the temperatures of maximum apparent density (2.41-2.52 g mL(-1)) in the range 1200-1300 A degrees C. The fine-grained sericite content and the presence of some mineralogical components contribute to the formation of mullite and the increase in the glassy phase by heating. Mullite is the only crystalline phase detected at 1400 A degrees C with good crystallinity. SEM revealed the dense network of rod-shaped and elongated needle-like mullite crystals in the thermally treated samples. These characteristics are advantageous when sericite clays are applied as ceramic raw materials.

Obituary Note: Prof. Jose Manuel Criado

Perez-Maqueda, L; Koga, N; Malek, J
Thermochimica Acta, 663 (2018) A1

ABSTRACT

The late Prof. Jose Manuel Criado (1944.6.13–2018.2.27)

It is with the profoundest regret that we must report the passing of Prof. José Manuel Criado on February 27, 2018 at the age of 73. We express our most sincere condolences to his family, colleagues and friends.

Prof. Criado was born in Sevilla, Spain, on June 13th, 1944. He studied chemistry at the University of Seville and recieved his PhD from the same university under the supervision of Prof. Francisco González García and Prof. José María Trillo. He held a position as assistant professor at the Department of Inorganic Chemistry of the University of Seville from 1968 until 1972. Then, he joined the Consejo Superior de Investigaciones Científicas (CSIC) or National Research Council of Spain. In this institution he was junior researcher, senior researcher and, from 1986, full professor. Moreover, he has been visiting professor in a number of international institutions such as Stanford University (USA), CNRS Thermodynamics and Microcalorimetry Center in Marseille (France), University of Salford (UK), Macaulay Research Institute (UK), Institute of Inorganic Chemistry (Czech Republic), University of Chile (Chile). He had long-lasting collaborations with scientists from all over the world and visited labs in many countries. For many years, he used to spend some weeks abroad in the frame of collaboration projects with a number of international research groups, of special importance where his projects with the Czech Republic or Chile that lasted for over 20 years. He also served as an editorial board member of Thermochimica Acta for a long time and contributed largely to the further development of our academic field.

First research works of Prof. Criado were done within the field of heterogeneous catalysis, but very soon, he got interested in reactivity of solids and thermal analysis. Thus, most of his scientific career has been devoted to the study of kinetics of solid-state processes and mechanochemisty. He published about 240 papers in international journals. In the field of kinetics of solid-state processes, he made significant contributions, such as showing the limitations of using single linear heating rate experiments for extracting kinetic parameters, the proposal of master curves for discerning the kinetic model followed by the process or the combined analysis of experimental data obtained under different heating schedules. Moreover, after learning about the sample controlled thermal analysis (SCTA) method directly from Prof. Rouquerol in Marseille (France) and Profs. Paulik brothers in Budapest (Hungary), he constructed several of these instruments and extended the use of SCTA to the kinetic analysis of heterogeneous reactions, highlighting its advantages over conventional heating. Additionally, he used the kinetic control of solid-state processes by SCTA for the preparation of a number of functional and structural materials with controlled microstructures and properties. In the field of mechanochemistry, he made substantial contributions to the preparation of materials by gas–solid reaction using high energy planetary ball mills specially modified by him to work under controlled gas atmosphere.

Probably, the main contribution of Prof. Criado as a scientist has been as teacher and mentor for many of us. Despite of spending most of his scientific career in a research center rather than in a university, his laboratories were always full of students, postdocs and visitors from all over the world. He devoted a great effort to motivate and stimulate young people to pursue a career in science. His enthusiasm for science was sincere, as he loved science and research. Thus, he worked until the very last days and, even, when he could not go to the institute because he did not feel well, he worked in a small lab at home. He was very generous and always shared his knowledge with others. Thus, he expended long hours teaching about kinetics, making the complex equations easy to understand. Only those with a deep knowledge have this ability! It is not rare that many of his former students, postdocs and coworkers have permanent positions as professors and scientist in a number of international institutions. Another significant feature of Prof. Criado was his hospitality. He and his wife Maria Jesús Dianez, who joined his research group few years ago, has always his home doors open to any coworker or visitor.

We will all miss him not only as a scientist with a deep knowledge but as a friend we loved so much.

Phase-pure BiFeO3 produced by reaction flash-sintering of Bi2O3 and Fe2O3

Mixed powders of Bi2O3 and Fe2O3 are shown to yield single-phase, dense nanostructured polycrystals of BiFeO3 in reaction flash sintering experiments, carried out by applying a field of 50 V cm(-1) and with the current limit set to 35 mA mm(-2). The furnace was heated at a constant rate with the reaction sintering taking place abruptly upon reaching 625 degrees C. Remarkably, an intermediate bismuth-rich phase of the oxide that forms just before reaching the flash temperature transforms, and at the same time sinters, into singlephase BiFeO3 within a few seconds after the onset of the flash. The BiFeO3 so produced is electrically insulating, a property that is critical to its applications. This one-step synthesis of single-phase polycrystals of complex oxides from their basic constituents, by reaction flash sintering, is a significant development in the processing of complex oxides, which are normally difficult to sinter by conventional methods.

Is an alumina-whisker-reinforced alumina composite the most efficient choice for an oxidation-resistant high-temperature ceramic?

The search of a competitive ceramic material for structural applications demands several requisites: a simple microstructure with easy reproducibility, good intrinsic mechanical properties and most of all, an optimal oxidation resistance. This later point is a challenging point for most ultrahigh refractory materials.
In this work an alumina (Al2O3) whisker-reinforced Al2O3 composite prepared by spark plasma sintering (SPS) is studied. It will be shown that, although the microstructure is quite similar to that of pure monolithic one, there is a notorious enhancement of the high-temperature deformation resistance, reaching up to one order of magnitude over the pure Al2O3 specimen. On the other hand, the activation energy of these composites increases notably. The results are explained in terms of an original model. A comparison with reported data shows that such composite is as efficient as a SiC-whisker-reinforced Al2O3 composite, with the advantage of its oxidation resistance and much less fabrication cost.

Spark plasma sintering of titanium nitride in nitrogen: Does it affect the sinterability and the mechanical properties?

Titanium nitride ceramics have an intrinsic interest due to its optical and structural applications. However, the conditions for sintering of dense pieces are not still clarified. This research work is focused on the spark plasma sintering (SPS) of near-fully dense fine-grained TiN. The main goal is giving a response to a longstanding debate: can the external atmosphere favor sintering? Different sintering atmospheres, either vacuum or a nitrogen flow, have been used during SPS heating to this purpose. X ray diffraction analysis has showed the presence of TiN as the main phase with traces of Ti4O7 in optimal SPS conditions (1600 °C, one minute dwell time). Our results show that the use of a nitrogen flow while heating can improve sinterability very slightly, but mechanical properties are essentially unaltered within the experimental uncertainty. The hardness reaches values as high as 20GPa whereas fracture toughness can be evaluated around 4 MPam1/2.

Synthesis of vaterite CaCO3 as submicron and nanosized particles using inorganic precursors and sucrose in aqueous medium

It is reported the synthesis of CaCO3 vaterite as stable nanoparticles and submicron-sized by a simple and relatively rapid procedure. XRD, SEM and FTIR techniques have been used to characterize the precipitated products. The synthesis is based on chemical precipitation of inorganic salt precursors, calcium nitrate tetra hydrate and sodium bicarbonate, and using the disaccharide sucrose as an additive in aqueous medium. The role of the disaccharide sucrose is to control the vaterite precipitation after nucleation and growth. It has been found that an increase in sugar concentration promotes the crystal precipitation of vaterite with spherulitic morphology, as revealed by SEM, and changed the surface of the precipitated particles. There is a significant difference between CaCO3 precipitation in the absence and presence of sucrose. Addition of 0% of sucrose leads to 83% of calcite as identified by XRD methods. In contrast, addition of 67% of sucrose in aqueous medium produces 100% vaterite. The present results may be useful to provide a quick, simple, inexpensive and novel method for the controlled synthesis of new advanced biomaterials based on vaterite particles without hazardous chemicals and inert atmosphere, with great possibilities for industrial scale production.

Self-propagating mechanosynthesis of HfB2 nanoparticles by a magnesiothermic reaction

A mechanically induced self-sustaining reaction (MSR) was used to synthesize hafnium diboride nanoparticles. Along this route, magnesium was selected as a robust reducing agent for co-reduction in boron and hafnium oxides in a combustive manner. Combustion occurred after a short milling period of 12 minutes. The hafnium diboride nanoparticles had a polygonal faceted morphology and were 50-250 nm in diameter. The assessment of the processing mechanism revealed that the initial combustive reduction in B2O3 to elemental B by Mg was the major step for progressing the overall reaction. After that, HfO2 can be reduced to elemental Hf, followed by the synthesis of HfB2 phase.

The use of coal fly ash (CFA) as raw material for the manufacture of two construction materials, fired clay bricks and silica-calcareous non-fired bricks, was investigated. Fired clay bricks were manufactured using a commercial clay and different waste ratios (0-50 wt%), moulded at 10 MPa and fired at 1000 degrees C (4 h). Silica-calcareous non fired bricks were prepared using two wastes as raw material: CFA and "geosilex"(G), a hidrated lime residue which comes entirely from acetylene industry waste. Different proportions CFA (80-30 wt%) G (20-70 wt%) were investigated. Raw materials were moulded at 10 MPa and cured in water at room temperature during 28 days. The results indicated that the incorporation of up to 20 wt% of CFA produced fired clay bricks with physical and mechanical properties similar to control bricks without waste. However, additions of a higher amount (30-50 wt%) of residue resulted in a more pronounced decrease in mechanical properties (between 25-50%) due to an increase in open porosity. The technological characterization of the silica-calcareous non fired bricks showed a reduction in the values of bulk density and water absorption when the coal fly ash content decreases. Silica-calcareous non-fired bricks containing between 40 and 60 wt% of CFA had the highest values of compressive strength in the range 46-43 MPa. These silica-calcareous non-fired bricks, 60CFA-40 G, 50CFA-50 G and 40CFA-60 G, presented the optimum amount of pozzolanic materials (SiO2 and Al2O3) in the coal fly ash and calcium hydroxide in the geosilex to give rise to the formation of calcium silicate hydrates and calcium aluminate hydrates, the phases responsible for the mechanical resistance increase of the construction materials. Therefore, CFA-clay fired bricks and silica-calcareous CFA-Geosilex non-fired bricks presented optimal technological properties that attain the quality standards.

{0 0 1} faceted TiO2 catalysts are hydrothermally synthesized by using titanium(IV) isopropoxide and butoxide precursors (ISO and BUT TiO2 samples) together with HF addition. Their activity and stability are evaluated in the catalytic condensation of light oxygenated organic compounds present in an aqueous model mixture simulating a real bio-refinery effluent, under moderate operation conditions. High {0 0 1} faceted TiO2 catalysts show organic products yields superior to those attained with other TiO2 samples (anatase, rutile, and P25). This enhanced catalytic activity relates to their physico-chemical and textural properties, such as high surface area (≈100 m2/g), regular morphology (platelets conformed by partially agglomerated TiO2 nanoparticles), and adequate Lewis acidity. XRD and Raman measurements evidence the unique presence of anatase crystalline phase in both ISO and BUT materials, in which the use of HF during synthesis produces the preferential growth of TiO2 crystals mainly exposing the {0 0 1} plane. This effective {0 0 1} facet exposition directly determines catalytic results. Moreover, TiO2 ISO catalyst shows outstanding stability under reaction conditions, maintaining practically unaltered their activity after several re-uses. In particular, Lewis acid sites present in TiO2 faceted materials are more stable in the presence of organic acids under aqueous environments. This opens new possibilities for the application of these materials in the valorization of light oxygenated compounds present in biomass-derived aqueous effluents.

This work reports the Calcium-Looping (CaL) multicycle performance under energy storage and CO2 capture conditions of different Al-composites prepared by milling mixtures of nanoalumina and natural limestone powders. The micro-and nanostructure of the composites have been analyzed by X-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy as affected by the type of CaL conditions employed, either for energy storage in Concentrated Solar Power (CSP) plants or for post-combustion CO2 capture. Two types of calcium aluminates are formed under these diverse CaL conditions. A calcium aluminate with ratio Ca/Al < 1 (Ca4Al6O13) is formed under CaL-CSP conditions, which helps stabilize the CaO microstructure and mitigate pore-plugging. On the other hand, a crystalline phase Ca3Al2O6 is formed (Ca/Al > 1) under CaL-CO2 capture conditions presumably due to the higher calcination temperature, which withdraws from the sorbent a relatively higher amount of active Ca. Moreover, the addition of nano-alumina, and the consequent generation of calcium aluminate, affects in a diverse way the microstructure and morphology of the CaO particles as depending on the CaL application, which critically modifies the performance of the composites.

Effect of Basicity on the Hydrolysis of the Bi(III) Aqua Ion in Solution: An Ab Initio Molecular Dynamics Study

Hydrolysis of the Bi(III) aqua ion under a range of solution conditions has been studied by means of ab initio molecular dynamics simulations. While the Bi(III) aqua ion is stable in pure water, there is an increasing degree of hydrolysis with the number of hydroxide anions in the medium. This is accompanied by a monotonic decrease of the total coordination number to an asymptotic value of similar to 6, reached under extreme basicity conditions. Comparison of the simulated Bi(III) hydrolyzed species with the experimental species distribution at different degrees of basicity suggests that, at the PBE/DFT level of theory here employed, liquid water shows an overly acidic character. Predictions of theoretical EXAFS and XANES spectra were generated from the AIMD trajectories for different Bi hydrolyzed species, [Bi(HO)(m)(H2O)(n)](3-m+), m = 0-3 and n = 7-2. Comparison with available experimental spectra is presented. Spectral features joined to the degree of hydrolysis and hydration are analyzed.

Influence of temperature on the biaxial strength of cemented carbides with different microstructures

The effect of the temperature on the mechanical strength of WC-Co cemented carbides with different microstructures (grain size and binder content) was evaluated. Biaxial flexural tests were performed on three cemented carbide grades at 600 °C using the ball-on-three-balls (B3B) method. Results were interpreted by Weibull statistics and compared to biaxial strength results at room temperature. A detailed fractographic analysis, supported by Linear Elastic Fracture Mechanics, was performed to differentiate the nature and size of critical defects and the mechanism responsible for the fracture. A significant decrease in the mechanical strength (around 30%) was observed at 600 °C for all grades of cemented carbides. This fact was ascribed to the change in the critical flaw population from sub-surface (at room temperature) to surface defects, associated with the selective oxidation of Co. Additionally, an estimation of the fracture toughness at 600 °C was attempted for the three cemented carbides, based upon the B3B strength results, the corresponding number of the tested specimens fragments and the macroscopic area of the B3B fracture surfaces. The fracture toughness was not affected by the temperature, at least up to 600 °C. In addition, the good agreement with the Single Edge Notch Beam toughness data suggests the possibility of employing this approach for fracture toughness evaluation of brittle materials under different testing conditions.

An ever more environmentally conscious society demands the use of green, sustainable and high-efficiency renewable energy resources. However, large-scale energy storage remains a challenge for a deep penetration of power produced from renewables into the grid. The Calcium-Looping (CaL) process, based on the reversible carbonation/calcination of CaO, is a promising technology for thermochemical energy storage (TCES) in Concentrated Solar Power (CSP) plants. Natural limestone to be used as CaO precursor is cheap, non-toxic and abundant. Nevertheless, recent works have shown that carbonation of CaO derived limestone at optimum conditions for TCES is limited by pore-plugging, which leads to severe deactivation for large enough particles to be employed in practice. In our work, we have synthesized inexpensive CaO/SiO2 composites by means of a biotemplate method using rice husk as support. The morphological and compositional features of the biomorphic materials synthesized help improve the CaO multicycle activity under optimum CSP storage conditions and for particles sufficiently large to be managed in practical processes.

High temperature creep of 20 vol%. SiC-HfB2 UHTCs up to 2000 degrees C and the effect of La2O3 addition

High temperature compressive creep of SiC-HfB2 UHTCs up to 2000 °C has been studied. Microstructural analysis after deformation reveals formation of new phases in the Hf-B-Si and Hf-B-Si-C systems, which are responsible for the poor creep resistance. RE oxide additions have a negative effect reducing the creep resistance of SiC-HfB2 UHTCs. A simplistic analysis for the required creep resistance is described, indicating that only SiC-HfB2 UHTCs could withstand re-entry conditions for 5 min in a single use. However, RE oxide addition to SiC-HfB2UHTCs does not provide the required creep resistance for them to be candidate materials for hypersonic applications.

A new combustion route for synthesis of TaB2 nanoparticles

Jalaly, M; Gotor, FJ
Ceramics International, 44 (2018) 1142-1146

ABSTRACT

Tantalum diboride (TaB2) nanoparticles were synthesized through a mechanically induced self-sustaining reaction (MSR). In this method, the ternary system of Mg/Ta2O5/B was employed in which, magnesium was used as a reducing agent for reduction of tantalum oxides in a combustive regime. The processing route of TaB2 by the solid-state combustion was very short-term and the product purification was extremely easy and rapid. The synthesis mechanism was studied and revealed that magnesiothermic reduction of tantalum oxide is the initiator of the total reaction, while borothermic reduction of the oxide may occur in parallel.

Surface-fluorinated TiO2 materials with high {001} facet exposure were prepared by a simple and high-yield preparation procedure. Faceted/fluorinated samples showed a high photocatalytic performance not only in oxidation processes, tested in phenol and methyl orange degradation, but also in a reduction process as Cr(VI) photoreduction. Reaction rates for these materials greatly exceeded the ones obtained for materials prepared without fluorine addition and for commercial TiO2 Degussa (Evonik) P25 used as reference photocatalyst. A broad characterisation of the samples allowed us to estimate the percentages of different facets and the amount and form in which the fluorine is found on the surfaces. Good photocatalytic behaviour can be ascribed to both high {001} facet exposure and adsorbed fluorine on the photocatalysts surfaces.

Development of a novel fcc structure for an amorphous-nanocrystalline Ti-33Nb-4Mn (at.%) ternary alloy

In this work, a novel amorphous-nanocrystalline titanium-niobium-manganese solid solution ternary alloy with a Ti-33Nb-4Mn (at.%) nominal composition was developed by a High-Energy Mechanical Alloying. Nb and Mn were added to the elemental Ti as a beta-phase (bcc) stabilizer and an amorphization promoter, respectively. The system evolved from the elemental Ti, Nb and Mn raw materials to a body centred cubic (bcc) TiNbMn alloy and, finally, to the formation of an original and stable face centred cubic (fcc) nanocrystalline TiNbMn alloy, not reported until now, at short milling time (20 h). This alloy remains invariant until 120 h. In turn, the partial amorphization of the system occurs and increases until at intermediate milling time (80 h). The production of both original fcc and the amorphous TiNbMn alloy may be beneficial for reducing the Young's modulus and improving the mechanical strength pursued for the Ti alloy. The optimal milling time respect to the amorphization, nanocrystalline size and Fe mount from milling media was 60 h and 80 h (TiNbMn60h and TiNbMn80h), with > 50 wt% of an amorphous phase and a crystalline domain size of approximately 5 nm.

TiC-Ni-based cermets were obtained by thermal explosion from different elemental mixtures (Ti, C, Ni and X, where X = Cr, Mo or W) and subsequently densified by hot-pressing under a cyclic load. The whole process was performed in a single stage in the same experimental device according to the following thermal and pressure procedure: a heating rate ramp up to 1573 K without applying any load followed by an isothermal dwelling under a compressive cyclic load of 32 MPa. The thermal explosion synthesis occurred during the heating ramp at a temperature close to 1273 K that was practically independent of the starting nominal composition. The influence of different refractory elements on the chemical composition and microstructure of cermets was studied. SEM characterization showed that only with Mo and W, the cermets developed the characteristic core-rim structure. A high densification was achieved, but decreased when the refractory elements were added. Nevertheless, in these cases higher hardness values were obtained.

The dizinc bond as a ligand: A computational study of elongated dizinc bonds

Following the synthesis of [Zn-2(eta(2)-C5Me5)(2)] (in short [Zn2Cp*(2)]) many complexes of the directly bonded Zn-Zn unit were prepared and characterized, leading to the recognition of an isolobal analogy between the Zn-Zn bond and the molecule of dihydrogen. Prompted by these results, we have investigated eta(2)-eta(2)-coordination of [Zn2Cp2] and [Zn2Ph2] (Cp = C5H5, Ph = C6H5) to several selected transition metal fragments and report herein the results of a QTAIM study of complexes [(ZnR)(2)Fe(CO)(4)], [(eta(2)-Zn2R2)M(CO)(5)]] and [(eta(2)-Zn2R2)Pd(PR'(3))(2)] (for R = Cp, Ph; M = Cr, Mo, W; and R' = F, H, Me). A decrease of rho(BCP), Delta(2) rho(BCP) and delocalization indexes delta(Zn, Zn), relative to corresponding values in the parent molecules of [Zn2Cp2] and [Zn2Ph2], accompanied dizinc coordination. In most cases the computed d(Zn, Zn) parameters were indicative of significant electron density sharing between the two Zn atoms. Nevertheless, the interaction with [Fe(CO)(4)] resulted in oxidative cleavage of the coordinated Zn-Zn bond, due to high pi backdonation to the sigma* Zn-2 MO as deduced from the delta(M, O-CO) index. The Zn-Zn bond critical points identified in our study are discussed. The computed Zn-Zn contacts concentrate in the range 2.44-2.58 angstrom, and we propose that this interval corresponds to elongated dizinc bonds.

The Calcium Looping (CaL) process, based on the carbonation/calcination of CaO, has been proposed as a feasible technology for Thermochemical Energy Storage (TCES) in Concentrated Solar Power (CSP) plants. The CaL process usually employs limestone as CaO precursor for its very low cost, non-toxicity, abundance and wide geographical distribution. However, the multicycle activity of limestone derived CaO under relevant CaL conditions for TCES in CSP plants can be severely limited by pore plugging. In this work, the alternative use of calcium-rich steel and blast furnace slags after treatment with acetic acid is investigated. A main observation is that the calcination temperature to regenerate the CaO is significantly reduced as compared to limestone. Furthermore, the multicycle activity of some of the slags tested at relevant CaL conditions for TCES remains high and stable if the treated samples are subjected to filtration. This process serves to remove silica grains, which helps decrease the porosity of the CaO resulting from calcination in the mesoporous range thus mitigating pore plugging.

Effect of acid-treatment and colloidal-processing conditions on the room temperature mechanical and electrical properties of 3YTZP/MWNT ceramic nanocomposites

Different colloidal powder processing routines have been used to prepare composites of 3 mol% Y2O3 -ZrO2 (tetragonal zirconia polycrystals, 3YTZP) with 2.5 vol% multiwall carbon nanotubes (MWNT) with the aim of achieving a homogeneous distribution of the MWNTs in the ceramic, eliminating agglomerates but also minimizing carbon nanotube (CNT) damage during processing. Modifications of the acid treatment applied to the nanotubes, including subjecting them to stirring or ultrasonic agitation, and use of acid or basic pH during composite powder mixing have been approached.
No MWNT damage during processing was detected by Raman spectroscopy. CNT bundles were found in all the composites forming different patterns depending on the processing route. Similar values of hardness were obtained for all the composites, while different anisotropy in fracture propagation was found when studying parallel and perpendicular directions to the sintering pressing axis on the cross sections of the composites due to the MWNT preferential alignment. The CNT bundles were found to act as fracture short paths. A similar anisotropic behavior was observed for the electrical conductivity. These results have been correlated to the different microstructures obtained in the composites prepared with different processing routines.

In this study we demonstrate the synthesis of quaternary semiconductor nanocrystals of stannite Cu2FeSnS4/rhodostannite Cu2FeSn3S8 (CFTS) via mechanochemical route using Cu, Fe, Sn and S elements as precursors in one-pot experiments. Methods of X-ray diffraction (XRD), nitrogen adsorption, high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) were applied to characterize properties of the unique nanostructures. Mechanochemical route of synthesis induced new phenomena like explosive character of reaction, where three stages could be identified and the formation of nanostructures 5-10 nm in size. By using XPS method, Cu(I), Fe(II), Sn(IV) and S(-II) species were identified on the surface of CFTS. The value of optical band gap 1.27 eV is optimal for semiconductors applicable as absorbers in solar cells. The significant photocatalytic activity of the CFTS nanocrystals was also evidenced. The obtained results confirm the excellent properties of the quaternary semiconductor nanocrystals synthesized from earth-abundant elements.

A characterization of ashes obtained by thermal treatments on greenhouse crops plant biomass residues is presented. The chemical analysis, by X-ray fluorescence (wavelength-dispersive X-ray fluorescence), and phase analysis, by X-ray diffraction, of the resultant ashes are reported. Thermal treatments of selected samples of these residues increase the relative amounts of inorganic Mg, Si, P, and S in the ashes, being these amounts as high as increasing temperature. As an opposite effect, Na, Cl, and K contents decrease as increasing temperature by a volatilization process of the chlorides, as confirmed by X-ray diffraction. The crystalline phase analysis of the ashes demonstrates the formation of inorganic constituents of the biomass, including alkaline chlorides and calcium salts (calcite, anhydrite, and apatite). Progressive thermal treatments induce the formation of new silicate phases (akermanite and grossularite) and silica (-quartz and cristobalite). Furthermore, the particle size of the starting biomass samples does not influence the evolution of the crystalline phases by thermal treatments. In contrast, a previous leaching using water and subsequent heating at 1,000 degrees C produces the formation of periclase (MgO), lime (CaO), and the silicate gehlenite, without the presence of anhydrite. This study is interesting for future investigations on the residues as a profitable biomass source for energy production and sustainable large-scale management. Some potential applications of the resultant ashes can be proposed.

Defect chemistry and electrical properties of BiFeO3

BiFeO3 attracts considerable attention for its rich functional properties, including room temperature coexistence of magnetic order and ferroelectricity and more recently, the discovery of conduction pathways along ferroelectric domain walls. Here, insights into the defect chemistry and electrical properties of BiFeO3 are obtained by in situ measurements of electrical conductivity, sigma, and Seebeck coefficient, a, of undoped, cation-stoichiometric BiFeO3 and acceptor-doped Bi1-xCaxFeO3-delta ceramics as a function of temperature and oxygen partial pressure pO(2). Bi1-xCaxFeO3-delta exhibits p-type conduction; the dependencies of s and a on pO(2) show that Ca dopants are compensated mainly by oxygen vacancies. By contrast, undoped BiFeO3 shows a simultaneous increase of s and a with increasing pO(2), indicating intrinsic behavior with electrons and holes as the main defect species in almost equal concentrations. The pO(2)-dependency of s and a cannot be described by a single point defect model but instead, is quantitatively described by a combination of intrinsic and acceptor-doped characteristics attributable to parallel conduction pathways through undoped grains and defect-containing domain walls; both contribute to the total charge transport in BiFeO3. Based on this model, we discuss the charge transport mechanism and carrier mobilities of BiFeO3 and show that several previous experimental findings can readily be explained within the proposed model.

Yttria tetragonal zirconia ceramic composites with 1, 2.5, 5 and 10 vol% nominal contents of graphene nanoplatelets (GNPs) were fabricated and characterized. First, the GNP dispersion in isopropanol was optimized to de-agglomerate the GNPs without damaging their structure. Then, submicrometric fully dense composites were obtained via spark plasma sintering (SPS) at 1250 degrees C with a 5 min holding time. The processing routine produced a nearly homogeneous GNP dispersion in the ceramic matrix, and the GNPs preferential orientation was perpendicular to the sintering compression axis. A ceramic grain refinement due to the GNPs was also detected. The Vickers hardness measured on the plane perpendicular to the sintering compression axis (basal plane) was lower than on the cross sections. This anisotropy increased with the increasing GNP content, while the average hardness decreased. The electrical conductivity was also highly anisotropic, up to seven times higher for the basal planes. The electrical percolation threshold for these composites was estimated to be between 2.2 and 4.4 vol% of the GNP measured content.

Thermochemical energy storage in Concentrated Solar Power plants by means of the Calcium-Looping process is a promising novel technology that would allow for a higher share of renewables. A main benefit of this technology is the use of widely available, non-toxic and environmentally friendly calcium carbonate minerals as raw materials to store energy. Efficient integration of the Calcium-Looping process into Concentrated Solar Power plants involves the endothermic calcination of CaCO3 in the solar receiver while the exothermic carbonation of CaO is carried out at high temperature under high CO2 partial pressure. The heat released by this reaction is carried out by the excess CO2 and employed for power generation by means of a closed CO2 cycle. This work explores the multicycle Calcium-Looping performance of naturally occurring CaCO3 minerals such as limestone, chalk and marble for thermochemical energy storage in Concentrated Solar Power plants. Despite their similar composition (almost pure CaCO3), these minerals exhibit a significant difference in their Calcium-Looping multicycle activity, which may be attributed to differences in particle size and microstructure. Pore plugging at the Calcium-Looping conditions for thermochemical energy storage tested in our work is a main limiting mechanism on the multicycle CaO carbonation activity.

Carbon nanofibers replacing graphene oxide in ceramic composites as a reinforcing-phase: Is it feasible?

In recent years, the interest of graphene and graphene-oxide has increased extraordinarily due to the outstanding properties concurring in this material. In ceramic science, the possibility of combining excellent electrical conductivities together with an enhancement of mechanical properties has motivated the research in fabrication of graphene oxide-reinforced ceramic composites despite the intrinsic difficulties for sintering. In this work a comparison is made between graphene oxide-reinforced alumina composites and carbon nanofiber-reinforced alumina ones. It will be concluded that the improvement of mechanical properties is scarce, if any. Since carbon nanofibers have also a good electrical conductivity their importance for future applications as a replacement of more sophisticated but expensive graphene-based ceramic composites will be stressed.

Influence of milling parameters on the solid-gas synthesis of TiCxN1-x by mechanically induced self-sustaining reaction

The synthesis of a titanium carbonitride solid solution (TiCxN1 − x) performed in a high-energy planetary mill by a solid-gas Mechanically induced Self-sustaining Reaction (MSR) was used to study the influence of a full set of experimental milling parameters on the ignition time (tig) as a measure of the mechanical dose rate provided by the mill. The highly exothermic Ti-C-N mixture was selected to ensure no competitiveness between MSR and diffusion-controlled routes under the milling conditions employed. The results showed that the dependence of tig on the spinning rate followed a potential function, with a potential factor higher than the value of 3 that would be obtained if a perfect collision model is assumed. The scalability of milling processes performed using planetary mills was confirmed. The results suggested that to define a milling experiment, it is necessary to provide not only the Ball-to-Powder mass Ratio (BPR) and spinning rate values, as is usually performed, but also the full set of milling parameters including the nature of the milling media (vial and balls), the number and size of balls, the mass of the powder charge, the pressure of the reactive gas and even the volume of the vial.

Ferroelectrics are important technological materials with wide-ranging applications in electronics, communication, health, and energy. While lead-based ferroelectrics have remained the predominant mainstay of industry for decades, environmentally friendly lead-free alternatives are limited due to relatively low Curie temperatures (T-C) and/or high cost in many cases. Efforts have been made to enhance T-C through strain engineering, often involving energy-intensive and expensive fabrication of thin epitaxial films on lattice-mismatched substrates. Here, a relatively simple and scalable sol-gel synthesis route to fabricate polycrystalline (Ba0.85Ca0.15)(Zr0.1Ti0.9)O-3 nanowires within porous templates is presented, with an observed enhancement of T-C up to similar to 300 degrees C as compared to similar to 90 degrees C in the bulk. By combining experiments and theoretical calculations, this effect is attributed to the volume reduction in the template-grown nanowires that modifies the balance between different structural instabilities. The results offer a cost-effective solution-based approach for strain-tuning in a promising lead-free ferroelectric system, thus widening their current applicability.

The present work is focused on thermochemical energy storage (TCES) in Concentrated Solar Power (CSP) plants by means of the Calcium-Looping (CaL) process using cheap, abundant and non-toxic natural carbonate minerals. CaL conditions for CSP storage involve calcination of CaCO3 in the solar receiver at relatively low temperature whereas carbonation of CaO is carried out at high temperature and high CO2 concentration to use the heat of reaction for power production by means of a CO2 closed power cycle. Under these conditions, large CaO particles derived from limestone to be used in industrial processes are rapidly deactivated due to pore plugging, which limits the extent of the reaction. This is favored by the relatively small pores of the CaO skeleton generated by low temperature calcination, the large thickness of the CaCO3 layer built upon the CaO surface and the very fast carbonation kinetics. On the other hand, at CaL conditions for CSP storage does not limit carbonation of CaO derived from dolomite (dolime). Dolime is shown to exhibit a high multicycle conversion regardless of particle size, which is explained by the presence of inert MgO grains that allow the reacting gas to percolate inside the porous particles.

Flash sintering of highly insulating nanostructured phase-pure BiFeO3

We show that BiFeO3, that is electrically homogeneous, is a good insulator, and has a low dielectric constant (the properties desired in its applications), can be produced by flash sintering, which is nominally difficult to achieve by conventional and spark plasma sintering processes. The flash-sintered specimens had a uniform microstructure with a nanometric grain size of similar to 20 nm.

Thermal study of residues from greenhouse crops plant biomass

The principal aim of this work is to examine the effect of thermal treatments using a muffle furnace (static heating) and by simultaneous TG/DTA (dynamic heating) on selected greenhouse crops plant biomass investigated here as the first time. The effect of fractionation by sieving (<25 and <2.5 mm), preheating at 150 °C for 48 h and leaching with water on the thermal behavior has been studied. The observation of similar profiles of mass variation corresponding to several samples heated in air up to 1150 °C allows to conclude that particle size did not influence the thermal evolution, but the effect of heating cycle is evidenced. Thermal analysis in air of a representative sample showed the several mass variation steps and DTA exothermic effects produced by the complex thermal decomposition and pyrolysis of the organic matter. Elemental analysis (CHNS and O) of the starting samples and thermally treated revealed the effect of the temperature, with formation of ashes with lower C content from 44.37 to 0.70 mass% as a minimum after elimination of organic matter by heating. Leaching increased the thermal mass variation as an effect of elimination of water-soluble components. According to the present results, the size fractionation of the greenhouse crops biomass did not influence the results of elemental composition. The present study has provided results of interest concerning this biomass source of renewable energy originated by the remains of tomato (Solanum lycopersicum L.), being estimated the highest of all the biomass produced by the greenhouse crops agricultural industry in Almería (SE Spain).

The epigraphic stela of Montoro (Cordoba): the earliest monumental script in Iberia?

A remarkable stela from Montoro, southern Spain, is unique in its morphology, epigraphic traits and landscape context. A programme of chemical characterisation, digital imaging, and geo-lithological and epigraphic analyses were conducted to determine its age and significance, and the results were integrated with data from archaeological investigations of the surrounding area. This multi-faceted approach allowed the stela to be interpreted within the context of early interactions between literate Mediterranean societies of the Late Bronze Age and Iron Age and non-literate Iberian societies. A key outcome of this research is a wider understanding of the complex patterns in the use and perception of early scripts.

Mesoporous ZnS-SiO2 nanocomposite was synthesized with a facile process. At first a large pore volume (1.86 cm(3).g(-1)), moderate pore size (about 12.8 nm) and moderate surface area (586 m(2).g(-1)) mesoporous SiO2 was synthesized in an acidic PH using cationic surfactant. ZnS nanoparticles were infiltrated in the porosities of the synthesized SiO2, with a room temperature post grafting method. The synthesized particles have been characterized with transmission electron microscopy (TEM), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET), furrier transformation infrared spectroscopy (FTIR) and diffuse reflectance spectroscopy (DRS). Results confirm the mesoporous characteristics of ZnS-SiO2 nanocomposite with specific surface area as high as 248 m(2).g(-1), pore volume of 0.89 cm(3).g(-1) and average pore diameter of about 14.4 nm. Simultaneous adsorption-photocatalytic behavior of this hybrid mesoporous nanocomposite for degradation of methylene blue (MB) was investigated. The efficiency of this material was compared with that of mesoporous SiO2 and also lone ZnS nanoparticles. Results showed that by using ultraviolet irradiation, ZnS-SiO2 can degrade greater than 85% of MB only after 3 min. The case for lone ZnS is less than 5% after 30 min. Degradation mechanism of MB using ZnS-SiO2 and ultraviolet radiation was explained with simultaneous adsorption and photocatalytic phenomena. Ultraviolet irradiation can degrade adsorbed MB of mesoporous SiO2 which can prevent it from saturation.

Characterization of of mechanosynthesized Bi1-xSmxFeO3 samples unencumbered by secondary phases or compositional inhomogeneity

High-quality samples, in terms of phase purity and dielectric properties, of composition Bi1-xSmxFeO3 (0.05 <= x <= 0.20) have for the first time been prepared by mechanosynthesis. Close inspection of the powder diffraction data, analysis via Rietveld refinement and TEM microscopy demonstrates that the Bi1-xSmxFeO3 samples contain only perovskite phases. Additionally, by a combination of Rietveld analysis, TEM, DSC, temperature-dependent XRD and permittivity data a tentative phase diagram has been proposed where the high temperature paraelectric phase Pnma has been confirmed for samarium substituted BiFeO3. Regarding the physical properties, the samples resulted to be electrically homogenous and highly insulating at room temperature, suggesting that other sources of conductivity, such as mixed valence of Fe associated with possible oxygen non-stoichiometry, have been avoided during the samples synthesis. In spite of the high quality of the samples, the dielectric and magnetic behaviour of the Bi1-xSmxFeO3 samples change only modestly on Sm substitution, with neither a great change in the resistivity or remnant magnetisation of Sm substituted samples in comparison with BiFeO3.

The Oxy-CaL process: A novel CO2 capture system by integrating partial oxy-combustion with the Calcium-Looping process

This paper proposes a novel CO2 capture technology from the integration of partial oxy-combustion and the Calcium -Looping capture process based on the multicycle carbonation/calcination of limestone derived CaO. The concentration of CO2 in the carbonator reactor is increased by means of partial oxycombustion, which enhances the multicycle CaO conversion according to thermogravimetric analysis results carried out in our work, thus improving the CO2 capture efficiency. On the other hand, energy consumption for partial oxy-combustion is substantially reduced as compared to total oxy-combustion. All in all, process simulations indicate that the integration of both processes has potential advantages mainly regarding power plant flexibility whereas the overall energy penalty is not increased. Thus, the resulting energy consumption per kilogram of CO2 avoided is kept smaller than 4 MI/kg CO2, which remains below the typical values reported for total oxy-combustion and amine based CO2 capture systems whereas CO2 capture efficiency is enhanced in comparison with the Calcium -Looping process.

A novel, simple and rapid route to the synthesis of boron cabonitride nanosheets: combustive gaseous unfolding

The ternary compound boron carbonitride (BCN) was synthesized in the form of few-layer nanosheets through a mechanically induced self-sustaining reaction (MSR). Magnesium was used to reduce boron trioxide in the presence of melamine in a combustive manner. The process to form the nanostructured material was very rapid (less than 40 min). The prepared powder was investigated by various techniques such as X-ray diffraction (XRD), Fourier Transform infrared (FTIR), Micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), and electron energy loss spectroscopy (EELS). The thermal stability and the optical behavior of the BCN nanosheets were also studied by thermal analysis and UV-vis spectroscopy, respectively. The formation mechanism of the nanosheet morphology was described in detail.

Effect of the impact energy on the chemical homogeneity of a (Ti,Ta,Nb)(C,N) solid solution obtained via a mechanically induced self-sustaining reaction

A titanium-tantalum-niobium carbonitride solid solution, (Ti,Ta,Nb)(C,N), was synthesised in a planetary mill via a mechanochemical process that involves a mechanically induced self-sustaining reaction (MSR) from stoichiometric Ti/Ta/Nb/C mixtures that are milled under a nitrogen atmosphere. The influence of the spinning rate of the planetary mill, which determines the impact energy of the milling process, on the ignition time (t(ig)) of the MSR process as well as the chemical homogeneity of the final product was analysed. The results indicated that the dependence of tig on the spinning rate followed a potential function with a potential factor of 4.85, implying a remarkable reduction in the milling time required to induce the self-sustaining reaction at increasing spinning rates (i.e., from 4200 min at 200 rpm to 15 min at 800 rpm). However, the chemical and structural characterisation of the obtained products at ignition without any extra milling treatment indicated that a single solid solution phase was only obtained at the lowest spinning rates (i.e., less than 300 rpm). At increasing rates, the relative amount of the intended solid solution phase continuously decreased, and new undesirable secondary phases were formed. Despite the long milling times required for the milling experiments that were performed at the slowest spinning rates, iron contamination from the milling media was negligible due to the low intensity milling regime.

Alumina (Al2O3) ceramic composites reinforced with either graphene oxide (GO) or carbon nanofibers (CNFs) were prepared using Spark Plasma Sintering. The effects of GO and CNFs on the microstructure and in consequence on their mechanical properties were investigated. The microstructure of the sintered materials have been characterized quantitatively prior to and after the creep experiments in order to discover the deformation mechanism. Graphene-oxide reinforced alumina composites were found to be more creep resistant than carbon nanofibers-reinforced alumina ones or monolithic alumina with the same grain size distribution. In all the cases, grain boundary sliding was identified as the deformation mechanism

Non-isothermal Characterization of the Precipitation Hardening of a Cu-11Ni-19Zn-1Sn Alloy

The precipitation hardening of a Cu-11Ni-19Zn-1Sn alloy has been studied by means of Differential Scanning Calorimetry (DSC), High-Resolution Transmission Electron Microscopy (HRTEM), and hardness measurements. The calorimetric curves, in the range of temperatures analyzed, show the presence of one exothermic reaction followed by an endothermic one. The exothermic DSC peak is due to the segregation of Cu2NiZn precipitates and it is associated to a noticeable improvement of the mechanical properties of the alloy. The endothermic effect is associated to the dissolution of the Cu2NiZn precipitates into the copper matrix for restoring the starting Cu-11Ni-19Zn-1Sn homogeneous solid solution. The reaction mechanisms of these processes have been proposed from the kinetic analysis of the exothermic and endothermic DSC signals. The results obtained point out that tin plays a decisive role on the precipitation hardening of the alloy, because age hardening is not observed in the case of a Cu-Ni-Zn ternary alloy of similar composition.

The Calcium Looping (CaL) process, based on the cyclic carbonation/calcination of CaO, has emerged in the last years as a potentially low cost technique for CO2 capture at reduced energy penalty. In the present work, natural limestone and dolomite have been pretreated with diluted acetic acid to obtain Ca and Ca-Mg mixed acetates, whose CO2 capture performance has been tested at CaL conditions that necessarily imply sorbent regeneration under high CO2 partial pressure. The CaL multicycle capture performance of these sorbents has been compared with that of CaO directly derived from limestone and dolomite calcination. Results show that acetic acid pretreatment of limestone does not lead to an improvement of its capture capacity, although it allows for a higher calcination efficiency to regenerate CaO at reduced temperatures (similar to 900 degrees C) as compared to natural limestone (>similar to 930 degrees C). On the other hand, if a recarbonation stage is introduced before calcination to reactivate the sorbent, a significantly higher residual capture capacity is obtained for the Ca -Mg mixed acetate derived from dolomite as compared to either natural dolomite or limestone. The main reason for this behavior is the enhancement of carbonation in the solid-state diffusion controlled phase. It is argued that the presence of inert MgO grains in the mixed acetate with reduced segregation notably promotes solid state diffusion of ions across the porous structure created after recarbonation.

Structure evolution in the LaMn1 − xFexO3 + δ system by Rietveld analysis

The synthesis of LaMn1 − xFexO3 + δ (0 ≤ x ≤ 1) solid solutions perovskite powder was carried out using high-energy milling from the constituent oxides, and further crystallization by high temperature treatment. The compositions of the crystalline phases as a function of x were determined by X-ray powder diffraction using a Rietveld refinement. The relationship between composition and structure was covered. This showed that LaMn1 − xFexO3 + δ exists with the rhombohedral structure (R-3c, 167) only below x = 0.3 and with the orthorhombic structure (Pnma, 62) over x = 0.7. The rhombohedral phase coexists with the orthorhombic phase between 0.4 < x < 0.6.

New findings on thermal degradation properties of fluoropolymers

In this paper, the thermal degradation properties of Viton A and Fluorel are investigated by both isoconversional and combined kinetic analysis methods using non-isothermal thermogravimetry technique. It has been found that the heating rate has little affect on the degradation residue of Fluorel and Viton A, where around 1.3% char was formed for Fluorel and 3.5% for Viton A. Different from the literature, the decomposition of Viton A should be considered as an overlapped dehydrofluorination and carbon chain scission process, with activation energy of 214 +/- 11 and 268 +/- 13 kJ mol(-1), respectively. The effect of dehydrofluorination on degradation of Fluorel is not so significant due to low content of H, and hence, it could be considered as a single-step mechanism with average activation energy of 264 +/- 14 kJ mol(-1). The thermal stability of Fluorel is much better than that of Viton A, and the predicted half-life is around 218 min for Fluorel and 49 min for Viton A at 420 A degrees C, which are consistent with experimental values. If using a single-step model as in the literature for Viton A, its half-life at 420 A degrees C would be underestimated for > 20%.

High surface area mesoporous ZnS nanoparticles (MZN) were obtained with the aid of the by-product of the synthesising reaction. This by-product, namely NaNO3, can be considered as a soft template responsible for the formation of pores. Ethanol and water were chosen as the synthesis media. Ultrasonic waves were used as an accelerator for the synthesis of MZNs. Photocatalytic activities of the synthesised samples for the degradation of methylene blue (MB) were investigated under ultraviolet irradiation. Synthesised specimens were characterised using field emission scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, diffuse reflectance spectroscopy, N-2-physisorption, and FT-IR spectroscopy. Results indicated that the synthesis media has a pronounced effect on the surface properties of the final porous particles by several mechanisms. The specific surface area of the MZN samples synthesised in water and ethanol were determined to be 53 and 201m(2)g(-1), respectively. The difference in the specific surface area was attributed to the weak solvation of S2- ions (Na(2)S5H(2)O in ethanol) and also to the by-product of the synthesis reaction. The photocatalytic behaviour of the mesoporous ZnS nanoparticles synthesised in these two media were investigated and the results have been interpreted with the aid of effective surface area, pore volume, and bandgap energy of the specimens.

In this study, we demonstrate a one-pot mechanochemical synthesis of the nanocomposite composed of stannite Cu2FeSnS4 and rhodostannite Cu2FeSn3S8 nanocrystals using a planetary ball mill and elemental precursors (Cu, Fe, Sn, S). By this approach, unique nanostructures with interesting properties can be obtained. Methods of XRD, Raman spectroscopy, UV-Vis, nitrogen adsorption, SEM, EDX, HRTEM, STEM, and SQUID magnetometry were applied. Quaternary tetragonal phases of stannite and rhodostannite with crystallite sizes 18-19 nm were obtained. The dominant Raman peaks corresponding to the tetragonal stannite structure corresponding to A-symmetry optical modes were identified in the spectra. The bandgap 1.25 eV calculated from UV-Vis absorption spectrum is very well-acceptable value for the application of the synthesized material. The SEM micrographs illustrate the clusters of particles in micron and submicron range. The formation of agglomerates is also illustrated on the TEM micrographs. Weak ferromagnetic properties of the synthesized nanocrystals were documented.

Effect of Thermal Pretreatment and Nanosilica Addition on Limestone Performance at Calcium-Looping Conditions for Thermochemical Energy Storage of Concentrated Solar Power

The share of renewable energies is growing rapidly, partly in response to the urgent need for mitigating CO2 emissions from fossil fuel power plants. However, cheap and efficient large-scale energy storage technologies are not yet available to allow for a significant penetration of renewable energies into the grid. Recently, a potentially low-cost and efficient thermochemical energy storage (TCES) system has been proposed, based on the integration of the calcium-looping (CaL) process into concentrated solar power plants (CSPs). The CaL process relies on the multicycle carbonation/calcination of CaO, which can be derived from calcination of widely available, cheap, and nontoxic natural limestone (CaCO3). This work explores the effect on the multicycle activity of limestone-derived CaO of thermal pretreatment under diverse atmospheres and the addition of nanosilica, which would be expected to hinder CaO grain sintering. Importantly, optimum CaL conditions for CSP energy storage differ radically from those used in the application of the CaL process for CO2 capture. Thus, calcination should be ideally carried out under low CO2 partial pressure at moderate temperature (below 750 degrees C), whereas CO2 concentration and temperature should be high for carbonation in order to maximize thermoelectric efficiency. When limestone is subjected to carbonation/calcination cycles at these conditions, its performance is critically dependent on the type of pretreatment. Our results indicate that the multicycle CaO activity is correlated with the size of the particles and the CaO pore size distribution. Thus, CaO activity is impaired as particle size is increased and/or CaO pore size is decreased. These observations suggest that pore plugging poses a main limitation to the multicycle performance of limestone-derived CaO at the optimum CaL conditions for TCES in CSPs, which is supported by scanning electron microscopy analysis. Strategies to enhance the performance of natural limestone at these conditions should be therefore oriented toward minimizing pore plugging rather than CaO grain sintering, which stands as the main limitation at CaL conditions for CO2 capture.

The mechanochemical synthesis of nanocrystalline CuFeSe2 particles prepared by high-energy milling in a planetary mill in an argon atmosphere from copper, iron, and selenium for 60 min is reported for the first time. The CuFeSe2 nanoparticles crystallize in tetragonal structure with mean crystallite size of about 32 +/- 1 nm. High resolution transmission electron microscopy measurements confirmed the presence of agglomerates which are formed by small nanocrystalline domains (5-40 nm). The magnetic data revealed that paramagnetic CuFeSe2 nanoparticles coexist with a small amount of ferromagnetic impurities at room temperature. The magnetic transition towards a weak ferromagnetic or ferrimagnetic behavior occurs in CuFeSe2 at approximately 79 K. The band gap of the CuFeSe2 particles is 0.95 eV which is wider than the band gap in bulk materials (0.16 eV), which could be in many aspects of application more beneficial.

Large-Scale Storage of Concentrated Solar Power from Industrial Waste

Deep penetration of renewable energies into the grid relies on the development of large-scale energy storage technologies using cheap, abundant, and nontoxic materials. Concentrated solar power (CSP) is particularly suitable to massively store thermal energy for dispatchable electricity generation. This is currently accomplished in a few demonstration plants by using molten salts albeit in a not competitive way yet. Process simulation studies indicate that thermochemical energy storage of CSP by means of the calcium looping (CaL) technology would reduce the cost of storage and increase the flexibility of energy supply provided that widely available and cheap CaO precursors with high and stable multicycle activity are used. In this work, we investigate the behavior of calcium rich steel slag at CaL conditions that would expectedly maximize the efficiency of CSP energy storage and power production. When treated with acetic acid, this nontoxic widely abundant waste yields a CaO rich solid with stable conversion near 0.8 over successive carbonation/calcination cycles at these CaL conditions

Ceramics of Ta-doping stabilized orthorhombic ZrO2 densified by spark plasma sintering and the effect of post-annealing in air

16 mol% Ta-doped ZrO2 powders were synthesized and densified by spark-plasma sintering (SPS) in vacuum, followed by post-SPS annealing in air, thus obtaining two ultrafine-grained ceramics consisting of Ta-doping stabilized orthorhombic ZrO2. The as-SPSed ceramic is black because it is actually a suboxide essentially with reduced cations and abundant oxygen vacancies, whereas the post-annealed ceramic is white because it is an oxide without vacancies and with only partially reduced cations. Both ceramics are relatively hard and brittle, but the as-SPSed ceramic was slightly more so, attributable to crystallographic and microstructural differences. Implications of interest for the ceramics community are discussed.

A Promising approach to the kinetics of crystallization processes: The sample controlled thermal analysis

Constant Rate Thermal Analysis (CRTA) method implies controlling the temperature in such a way that the reaction rate is maintained constant all over the process. This method allows determining simultaneously both the kinetic parameters and the kinetic model from a single experiment as the shape of the CRTA -T curves strongly depends on the kinetic model. CRTA method has been developed in the market only for thermogravimetric and thermodilatometric systems and, therefore, its use has been limited until now to the kinetic study of processes involving changes in mass or size of the samples, respectively. To overcome this obstacle, a method has been developed in this work for using the DSC signal for controlling the process rate in such a way that CRTA would be applied to the kinetic analysis of either phase transformations or crystallizations. The advantages of CRTA for performing the kinetics of crystallization processes have been here successfully demonstrated for the first time after selecting the crystallization of zirconia gel as test reaction.

Samples in the system Bi1-xYbxFeO3 (0.02 <= x <= 0.07) have for the first time been prepared by mechanical activation followed by sintering. XRD and DSC measurements show that the solubility limit of ytterbium in the R3c Bi1-xYbxFeO3 system is reached at x similar to 0.03. Higher ytterbium contents lead to a two-phase mixture of a main R3c phase of approximate composition Bi0.97Yb0.03FeO3 and ytterbium enriched secondary phases that cannot be readily indexed or quantified due to their small amount. DSC and temperature-dependent XRD showed that while the magnetic ordering temperature, T-N, was unaffected by Yb substitution, the ferroelectric ordering, T-C, declined. Temperature-dependent XRD patterns show that all samples exhibit rhombohedral R3c to orthorrhombic Pnma phase transitions. Diffuse reflectance spectroscopy suggests the potential use of the samples in photocatalytic applications due to their low band gap energy. Impedance spectroscopy and magnetic measurements show that samples are electrically homogenous and highly insulating, exhibiting antiferromagnetic behaviour at room temperature.

A new family of cermets: Chemically complex but microstructurally simple

Cermets based on Ti(C,N) have interesting properties, such as high wear resistance, high chemical stability and good mechanical strength at high temperature, but to become a viable alternative to cemented carbides, the fracture toughness and damage tolerance must be significantly improved. Complete solid-solution cermets (CSCs) have been proposed to further improve the mechanical properties of these materials. However, to develop this family of cermets with a high level of quality and reliability, using pre-fabricated complex carbonitrides is necessary instead of unalloyed mixtures as the raw ceramic material. A mechanochemical process called mechanically induced self-sustaining reaction (MSR) is suitable to obtain these complex carbonitrides with high stoichiometric control. On the other hand, high entropy alloys (HEAs), which can also be obtained by mechanochemical processes, are a good candidate to replace the current binder phase in cermets because they exhibit high strength and ductility at high temperature and good resistance to both wear and corrosion. In this work, a new family of CSCs based on (Ti,Ta,Nb)CxN1-x, with HEAs belonging to the Fe-Co-Ni-Cr-Mn-V system as the binder phase is developed by mechanochemical processes. With only two constituent phases, these cermets have a simple microstructure but a high compositional complexity because both the ceramic and binder phases are complex solid solutions with at least five components.

Irradiated fuel pellets present radial gradient porosity. CeO2 has been proven as a surrogate material to understand irradiated mixed oxide (MOX) due to its similar structural and mechanical properties. A novel compaction device was developed to produce CeO2 cylindrical pellets with controlled radial porosity. Three blends of CeO2 with different binder contents (0.5, 3 and 7.5 vol.% of ethylene-bis-stearamide, EBS) were prepared and used to obtain three different porosities for the core, intermediate and outer rings of pellets, respectively. Different compaction pressures were employed in each region to get the intended porosities. The whole pellet was subjected to a heating rate up to 500 degrees C to remove the EBS binder. Finally, a pressureless sintering step was performed at 1700 degrees C for 4 h. A microstructural characterization was performed in the three areas, including grain size and porosity. Mechanical properties like hardness, fracture toughness and tribo-mechanical response, as scratch resistance, were also determined. Pellets fabricated from this device have shown microstructural and mechanical properties with a good correlation to those of irradiated nuclear fuel.

In this work, a new photocatalyst based on bismuth titanates with outstanding visible photocatalytic activity was prepared by a facile hydrothermal method. The synthesised material showed visible activity as high as UV activity of commercial TiO2 P25 under the same experimental conditions for phenol degradation. A wide characterisation of the photocatalyst was performed. The material was composed of three phases; majority of Bi20TiO32 closely interconnected to Bi4Ti3O12 and amorphous TiO2. The high visible activity showed by this material could be ascribed to a combination of several features; i.e. low band gap energy value (2.1 eV), a structure allowing a good separation path for visible photogenerated electron-holes pairs and a relatively high surface area. This photocatalyst appeared as a promising material for solar and visible applications of photocatalysis.

The method for the deconvolution of overlapping DSC peaks here proposed has been used by the first time for the quantitative determination of the enthalpies associated to the phase transitions undergone during the aging of an alloy. They have been determined the enthalpies evolved along the first and the second overlapping DSC traces of Cu-10 wt%Ni-5.5 wt%Sn alloy, which are associated, respectively, to the spinodal decomposition of the alloy and the segregation of a DO22 (CuxNi1-x)(3)Sn tetragonal phase. The fraction of the DO22 phase (responsible of the aging hardening of this alloy) has been successfully determined from DSC as a function of the annealing treatment, while TEM and XRD failed for this purpose. It has been demonstrated that a threshold higher than 50% of crystallization of the DO22 phase is required for achieving a significant increase of the hardness as a function of the crystallization percentage. These results suggest that microcalorimetric measurement can be a powerful tool to establish quantitative relationships between the mechanical, electrical or functional properties of alloys and their structural changes undergone by aging.

Densification of alumina whisker-reinforced alumina ceramics by spark plasma sintering (SPS) has been investigated with the aim of obtaining a fine-grained microstructure and also studying the effect of whisker addition on the room-temperature mechanical properties. It was found that whisker addition retards slightly the sinterability of alumina by whisker hindering of particle rearrangement. Besides, the internal stress on the alumina matrix particles reduced due to the presence of a whisker network structure of strong rigid boundaries. Nevertheless near fully-dense and fine-grained alumina ceramics with alumina whisker content between 3 wt% and 10 wt% could be obtained under appropriate SPS conditions. The hardness of alumina ceramics with 3 wt% was comparable to that of pure alumina ceramics (similar to 26 GPa) whereas its fracture toughness (5.6 MPa m(1/2)) was higher (4.2 MPa m(1/2)). Crack bridging by well-dispersed whiskers and whiskers pull-out were identified as the main toughening mechanisms.

Analytical investigation of Mudejar polychrome on the carpentry in the Casa de Pilatos palace in Seville using non-destructive XRF and complementary techniques

The pigments, execution technique and repainting used on the polychrome wood ceilings and doors in the Casa de Photos (Seville, Spain) were studied using portable X-ray fluorescence equipment. Cross-sections of small samples were also analysed by optical microscopy, SEM with EDX analysis, micro-Raman and micro-infrared spectroscopy and X-ray diffraction. These carpentry works are magnificent examples of the Mudejar art made in Spain in the early 16th century. Portable X-ray fluorescence gave good information on the different components of the polychrome. The SEM-EDX study of the surfaces of small samples gave information on their components and also characterized the compounds that had been deposited or formed by environmental contamination or by the alteration of some pigments. The SEM-EDX study of cross-sections facilitated the characterization of all layers and pigments from the support to the most external layer. The following pigments were characterized: red (cinnabar/vermillion, lead oxide, iron oxides and orpiment/realgar), black (carbon black), white (white lead and titanium barium white), yellow-orange-red-brown (orpiment/realgar and iron oxides), green (chromium oxide), blue (indigo blue and ultramarineblue), and gilding (gold leaf on bole). False gold, bronze and brass were also found. The pigments were applied with the oil painting technique over a support layer that had been primed with animal glue. This support layer was gypsum in some cases and white lead in others. This study is essential to the polychrome conservation of the studied artwork, and it will help clarify uncertainties in the history and painting of Mudejar art.

Structural and Chemical Characteristics of Sisal Fiber and Its Components: Effect of Washing and Grinding

This work covers the study of microstructural changes of natural sisal fibers induced by different conditioning pre-treatments: mechanical grinding, cryogenic grinding, and hot waterwashing. The aim of the work is to clarify the effects of the pre-treatments on crystallinity and infrared spectra of sisal. Scanning electron microscopy results allowed to identify morphological changes on the fiber surface. Deeper changes of chemical origin were studied by attenuated total reflectance/Fourier transform infrared spectroscopy (FTIR) and focused on the main components of cellular walls: cellulose, lignin, and xylan. The work was complemented with crystallinity index (I-c) data determined by two very different methods: the widely used for lignocellulosic fibers Segal equation based on X-ray diffraction measurements, and the other based on FTIR through the 1430/900 cm(-1) band intensity ratio, which is mostly used with cellulosic samples.

The calorimetric analysis as a tool for studying the aging hardening mechanism of a Cu-10wt%Ni-5.5wt%Sn alloy

The transformations of a Cu-10wt%Ni-5.5wt%Sn alloy as a function of the aging time in the range from room temperature up to 600 degrees C have been followed by Differential Scanning Calorimetry (DSC). The results obtained have shown that this alloy undergone two overlapping exothermic phase transitions with DSC peaks at 208 degrees C and 305 degrees C, respectively, followed by an endothermic phase transformation with a DSC peak at 526 degrees C. The structural analysis by TEM, ED, EDX and XRD of the intermediates phases previously discriminated by DSC suggests that the first exothermic peak is associated to the spinodal decomposition of the sample, while the second one is associated to the segregation of a DO22 (Cu-x-Ni1-x)(3)Sn tetragonal phase coherent with the alpha-Cu structure of the starting alloy. The endothermic peak has been associated to the precipitation of cubic DO3 nanocrystals from the DO22 phase previously formed. The microhardness measurements carried out in combination with the structural characterization demonstrate that the aging hardening of the alloy under study is exclusively due to the formation of the coherent DO22 phase. The DO22/DO3 transition leads to a dramatic drop of the hardness of the alloy.

The polymer-to-ceramic transformation kinetics of two widely employed ceramic precursors, 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane (TTCS) and polyureamethylvinylsilazane (CERASET), have been investigated using coupled thermogravimetry and mass spectrometry (TG-MS), Raman, XRD and FTIR. The thermally induced decomposition of the pre-ceramic polymer is the critical step in the synthesis of polymer derived ceramics (PDCs) and accurate kinetic modeling is key to attaining a complete understanding of the underlying process and to attempt any behavior predictions. However, obtaining a precise kinetic description of processes of such complexity, consisting of several largely overlapping physico-chemical processes comprising the cleavage of the starting polymeric network and the release of organic moieties, is extremely difficult. Here, by using the evolved gases detected by MS as a guide it has been possible to determine the number of steps that compose the overall process, which was subsequently resolved using a semiempirical deconvolution method based on the Frasier-Suzuki function. Such a function is more appropriate that the more usual Gaussian or Lorentzian functions since it takes into account the intrinsic asymmetry of kinetic curves. Then, the kinetic parameters of each constituent step were independently determined using both model-free and model-fitting procedures, and it was found that the processes obey mostly diffusion models which can be attributed to the diffusion of the released gases through the solid matrix. The validity of the obtained kinetic parameters was tested not only by the successful reconstruction of the original experimental curves, but also by predicting the kinetic curves of the overall processes yielded by different thermal schedules and by a mixed TTCS-CERASET precursor.

Under Calcium-Looping “realistic” operation conditions (high CO2 concentration and temperature), the multicycle CO2 capture capacity performance of CaO derived from limestone and dolomite is inversely related to its crystallite size. Ball-milling the raw sorbents results in the formation of larger nascent CaO nanocrystals during the calcination. Constraint sintering effect due to inert compounds such as dolomitic MgO mitigates the inactivation.

The use of lipid nanosystems as drug delivery to the central nervous system may be advantageous over the current strategies. The aim of this study was to develop and characterize functionalized liposomes for treatment of brain diseases. The covalent method of coupling IgG to liposomes via the derivatized lipid 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-[4-(p-maleimidophenyl)butyramide](MPB-PE) was investigated. Optimized coupling conditions are shown to result in the efficient conjugation of IgG to liposomes containing low concentrations of MPB-PE (3/1 SH:IgG). The qualitative analysis has shown that after the extrusion process, more homogeneous populations of vesicles have been obtained with a nanometric size suitable to be effective to further anchor the protein. Negative values of zeta potential demonstrate that they are stable systems. Lyophilization was used to maintain the stability of the formulation. These very interesting results encourage further investigations to formulate peptide- and protein-loaded immunoliposomes, making targeting of liposomes as an attractive approach for brain drug delivery.

This study attempts to establish the advantages and limitations of the combined use of portable UV–Vis-FORS and XRF-XRD portable equipment for the non-invasive characterisation of pigments from Roman wall paintings from Seville, Spain, dated to the first and second century AD. XRD revealed the presence of calcite, dolomite and aragonite, indicating the colour white. Egyptian blue was identified using FORS and XRF, and additional information was obtained with XRD. For the colour green, FORS and mainly FTIR and colorimetry enabled the distinction between glauconite and celadonite, although other techniques were necessary to classify all components of the green areas by determining the presence of cuprorivaite, chlorite and chromium. For the colours yellow and red, the presence of goethite, yellow ochre, cinnabar and haematite was confirmed using FORS and XRF in some cases; the results were corroborated by XRD. Chromatic characterisation and the values of inflection points of FORS spectra enabled a better differentiation between reddish colours (orange, brown, purple and pink). The XRD and XRF techniques revealed that violet was created by mixing red haematite and Egyptian blue and slight variations in FORS spectra confirmed this.

The use of lipid nanosystems as drug delivery to the central nervous system may be advantageous over the current strategies. The aim of this study was to develop and characterize functionalized liposomes for treatment of brain diseases. The covalent method of coupling IgG to liposomes via the derivatized lipid 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-[4-(p-maleimidophenyl)butyramide](MPB-PE) was investigated. Optimized coupling conditions are shown to result in the efficient conjugation of IgG to liposomes containing low concentrations of MPB-PE (3/1 SH:IgG). The qualitative analysis has shown that after the extrusion process, more homogeneous populations of vesicles have been obtained with a nanometric size suitable to be effective to further anchor the protein. Negative values of zeta potential demonstrate that they are stable systems. Lyophilization was used to maintain the stability of the formulation. These very interesting results encourage further investigations to formulate peptide- and protein-loaded immunoliposomes, making targeting of liposomes as an attractive approach for brain drug delivery.

In this work, several modifications of the colloidal processing technique and spark plasma sintering (SPS) to prepare yttria tetragonal zirconia composites (YTZP) with single walled carbon nanotubes (SWNT) have been tested with the aim of eliminating SWNT agglomerates. These modifications include high versus low energy ultrasonic agitation during colloidal processing, lyophilization of the 3YTZP/SWNT slurry and electrical insulation during sintering of the composites. Semi-quantitative microstructural characterization of the carbon nanotube distribution in the sintered composites showed that high energy ultrasonic agitation reduces drastically agglomerate size. Lyophilization of the mixed suspensions avoids SWNT bundle size growth. Combination of both produces an enhanced carbon nanotube network distribution along the grain boundaries (GB) due to the absence of carbon nanotube agglomerates and to a limited SWNT bundle size. This results in an increase of the real SWNT content in the GBs up to nominal SWNT content and therefore an enhanced SWNT efficiency in the composites. The agglomerate-free highly-dispersed composites exhibit a decrease in density together with grain size refinement, a decrease in room temperature hardness, an increase in flexural strength and a most significant increase in room temperature electrical conductivity. Improved SWNT distribution also lowers electrical percolation threshold to a very low level in SWNT ceramic composites, <1 vol% SWNT.

Magnesium hydride for energy storage applications: The kinetics of dehydrogenation under different working conditions

A new approach to the kinetics of magnesium hydride dehydrogenation is considered. A model able to predict the dehydrogenation under different experimental conditions has been proposed. A new combined kinetic analysis method, which considers the thermodynamic of the process according to the microreversibility principle, has been used for performing the kinetic analysis of data obtained under different thermal schedules at hydrogen pressures ranging from high vacuum up to 20 bar.
The kinetic analysis shows that the dehydrogenation mechanism of magnesium hydride depends on the experimental conditions. Thus, the reaction follows a first order kinetics, equivalent to an Avarmi-Erofeev kinetic model with an Avrami coefficient equal to 1, when carried out under high vacuum, while a mechanism of tridimensional growth of nuclei previously formed (A3) is followed under hydrogen pressure. An explanation of the change of mechanism is given. It has been shown that the activation energy is closed to the Mg-H bond breaking energy independently of the hydrogen pressure surrounding the sample, which suggests that the breaking of this bond would be the rate limiting step of the process. The reliability of the calculated kinetic parameters is tested by comparing simulated and experimental curves.

On the relevant role of solids residence time on their CO2 capture performance in the Calcium Looping technology

The multicycle CO2 capture performance of CaO derived from natural limestone and dolomite has been investigated by means of thermogravimetry under realistic Calcium-Looping conditions, which necessarily involve high CO2 concentration and high temperatures in the calcination stage and fast transitions between the carbonation and calcination stages. Natural dolomite allows reducing the calcination temperature as compared to limestone while high calcination efficiency is maintained. This could help reducing the energy penalty of the CaL process thus further enhancing the industrial competitiveness for the integration of this technology into fossil fuel power plants. Importantly, the CO2 capture capacity of the sorbents is critically affected by the solids residence time in the carbonation and calcination stages within the feasible range in practice. Thus, carbonation/calcination residence times play a critical role on the multicycle CO2 capture performance, which has been generally dismissed in previous studies. A main observation is the enhancement of carbonation in the solid-state diffusion controlled phase, which is against the commonly accepted conception that the only relevant phase in the carbonation stage is the fast reaction-controlled stage on the surface of the solids. Thus, the CO2 capture efficiency may be significantly enhanced by increasing the solids residence time in the carbonator.

Assessment of the performance of commonly used DFT functionals vs. MP2 in the study of IL-Water, IL-Ethanol and IL-(H2O)(3) clusters

López-López, A., Ayala, R.
Journal of Molecular Liquids, 220 (2016)

ABSTRACT

We present a comparative study of the accuracy of different DFT approaches vs. MP2 for evaluating ionic liquids (ILs) + cosolvent. Namely, we are interested in [XBmim] + cosolvent (X being Cl-, BF4-, PF6-, and CH3SO3- anions and cosolvent being water or ethanol) and [XBmim] + (H2O)(3) clusters. In this study the B3LYP, B3LYP-D3, M06, M06-2X and M06-HF functionals with Pople and Dunning basis sets are considered. We find that the influence of the basis sets is a factor to take into consideration. As already seen for weakly bonded systems when the basis set quality is low the uncorrected counterpoise (unCP) or averaging counterpoise (averCP) energies must be used due to cancellation errors. Besides, the inclusion of extra diffuse functions and polarization is also required specially in the case of ILs interacting with water clusters. The B3LYP functional does not reproduce either the structure or the interaction energies for ILs + H2O and ILs + EtOH aggregates, the energetic discrepancies being more significant than the structural ones. Among the dispersive corrected functionals, M06-2X results resemble to a great extent the reference data when the unCP interaction energies are considered for both water and ethanol. In turn, M06 and B3LYP-D3 functionals are the best option for ILs containing polar and non-polar anions, respectively, whether the averCP interactions energies are taking into consideration. From the structural point of view, B3LYP and M06 functionals describe more open structures whereas B3LYP-D3, M06-2X and M06-HF structures resemble quite well MP2 results. When the number of water molecules increases the H bonding motif gains importance and the effect depends on the underlying functional. Only M06-2X and M06-HF behaviour is similar to that observed for one water molecule. This is important because to describe ILs-cosolvent solutions is not only necessary to take into account the ILs-cosolvent interactions but also the cosolvent-cosolvent ones in the ensemble of the system.

Correlation between chemical and mineralogical characteristics and permeability of phyllite clays using multivariate statistical analysis

Phyllite clays are applied as a layer on a surface to be waterproofed and subsequently compacted. For this purpose, phyllite clays deposits can be grouped by their chemical and mineralogical characteristics, and these characteristics can be connected with their properties, mainly permeability, in order to select those deposits with the lowest permeability values. Several deposits of phyllite clays in the provinces of Almeria and Granada (SE Spain) have been studied. The results of applying a multivariate statistical analysis (MVA) to the chemical data analysed from 52 samples determined by XRF, mineralogical analysis by XRD and permeability are reported. Permeability, a characteristic physical property of phyllite clays, was calculated using the results for experimental nitrogen gas adsorption and nitrogen adsorption-desorption permeability dependence. According to the results, permeability values differentiated two groups, i.e. group 1 and group 2, with two subgroups in the latter. The influence of chemical as well as mineralogical characteristics on the permeability values of this set of phyllite clays was demonstrated using a multiple linear regression model. Two regression equations were deduced to describe the relationship between adsorption and desorption permeability values, which support this correlation. This was an indication of the statistical significance of each chemical and mineralogical variable, as it was added to the model. The statistical tests of the residuals suggested that there was no serious autocorrelation in the residuals.

On the Multicycle Activity of Natural Limestone/Dolomite for Thermochemical Energy Storage of Concentrated Solar Power

Cheap, efficient, and non-toxic energy storage technologies are urgently needed to handle the rapidly increasing penetration of intermittent renewable energies into the grid. This work explores the use of limestone and dolomite for energy storage in concentrated solar power (CSP) plants by means of the calcium looping (CaL) process based on the multicycle carbonation/calcination of CaO. An efficient integration of the CaL process into CSP plants involves high temperature carbonation and calcination at moderate temperatures in a close CO2 cycle for power generation. These conditions differ from those of the CaL process for CO2 capture, which lead to CaO deactivation as extensively reported in recent years. In contrast, we show that limestone- and dolomite-derived CaO give rise to a high residual conversion at CaL-CSP conditions and in short residence times, which would facilitate the development of a competitive and clean CSP technology with permanent energy storage.

A new approach to the determination of the synthetic or natural origin of red pigments through spectroscopic analysis

This work suggests a way of differentiation between the natural or synthetic origin of inorganic materials that were historically used in the Cultural Heritage field. An exhaustive review of different reported procedures of synthesis of pigments was conducted, as well as a review of the accompanying minerals in case of natural pigments. The natural or synthetic origin of the pigments studied in this work was performed through the characterization of the accompanying minerals, in the case of the natural pigments, or the trace elements that are present as part of synthesis by-products or washing/purifying reagents and/or reactants that have only been partly removed in the final steps of these processes. This work characterized red pigments due to their wide variety, complexity and possibility of use in different mixtures. The following pigments were studied: cinnabar-vermilion, red lead and iron pigments. Also mixtures of these pigments between them and with red lake were also studied. Natural cinnabar was accompanied by silicon oxide (opal, chalcedony or quartz), calcite, clay minerals and, sometimes, pyrite. K together with S indicated a synthetic pigment (vermilion) obtained through the wet method. Nevertheless, K has not been found in layers containing only vermilion in our samples. The presence of Sn in some cases indicated vermilion that came from the dry process. K from the synthesis always appeared in the red lead pigment. The red natural ochre was confirmed by presence of clay minerals and iron. It should be said that Ca and S, and sometimes Al and K, were usually found in Mars red pigment. The presence of Al and Ca allowed the identification of carmine lake.

Constant rate thermal analysis of a dehydrogenation reaction

The Constant Rate Thermal Analysis (CRTA) procedure has been employed for the first time to study the kinetics of MgH2 dehydrogenation by thermogravimetry under high vacuum. CRTA implies controlling the temperature in such a way that the decomposition rate is maintained constant all over the process, employing the mass change as the experimental signal proportional to the reaction rate. The CRTA curves present a higher resolution power to discriminate the kinetic model obeyed by the reaction in comparison with conventional heating rate curves. The combined kinetic analysis has been applied to obtain the kinetic parameters, which show that MgH2 decomposition under high vacuum obeys first-order kinetics (F1). It has been proposed that the dehydrogenation of MgH2 under high vacuum takes place by instantaneous nucleation in the border line of the bidimensional crystallites followed by the growth of the nuclei.

A flexible and robust piezoelectric nanogenerator (NG) based on a polymer-ceramic nanocomposite structure has been successfully fabricated via a cost-effective and scalable template assisted hydrothermal synthesis method. Vertically aligned arrays of dense and uniform zinc oxide (ZnO) nanowires (NWs) with high aspect ratio (diameter similar to 250 nm, length similar to 12 mu m) were grown within nanoporous polycarbonate (PC) templates. The energy conversion efficiency was found to be similar to 4.2%, which is comparable to previously reported values for ZnO NWs. The resulting NG is found to have excellent fatigue performance, being relatively immune to detrimental environmental factors and mechanical failure, as the constituent ZnO NWs remain embedded and protected inside the polymer matrix.

In this work a cheap detector of organic molecules is developed. It comprises a cellulose fiber doped with a mixture of magnetite and reduced silver nanoparticles, the latter ones synthesized anew. The nanoparticles and the fiber were characterized with well-established spectroscopic, microscopic and magnetic techniques, namely infrared, UV–vis spectroscopies, vibrating sample magnetometry and electronic microscopies. The so-obtained doped-fibers were tested as surface enhanced Raman spectroscopy detector in aqueous samples with a diluted mixture of two pollutant models (rhodamine 6G and picric acid), being able to differentiate between both organic compounds. Hence, the nanoparticle-impregnated fiber is proposed as a reliable preliminary qualitative and semiquantitative test of the presence of specific organic molecules in solutions. Moreover, the magnetite nanoparticles provide the detector with a saturation magnetization value that enables the separation of the fiber from the solution with the aid of a commercial magnet.

Targeted multifunctional tannic acid nanoparticles

Tannic acid (TA) has multiple effects against cancer, being especially promising in those types that overexpress the epidermal growth factor receptor (EGFR), as TA modulates its activation and downstream signaling pathways, triggering apoptosis. Nonetheless, despite the important role of this receptor in the pathogenesis and progression of a wide variety of tumors, no TA systems targeted to this receptor have been described yet. In this work, we synthesize, characterize by physico-chemical techniques and study the cytotoxic effect and cell uptake of TA nanoparticles targeted to EGFR in both tumoral and normal human skin cells. Our nanoparticles exhibited an extremely high entrapment efficiency, and were only toxic for the tumoral cells. The uptake assay demonstrated that nanoparticles are able to enter the cells through a receptor-mediated mechanism. Furthermore, we have included fluorescent markers in these nanoparticles to combine imaging and therapeutic applications, thus building effectively a multifunctional tool for biomedicine.

Use of steel slag for CO2 capture under realistic calcium-looping conditions

In this study, CaO derived from steel slag pretreated with diluted acetic acid has been tested as a dry sorbent for CO2 capture under realistic Ca-Looping (CaL) conditions, which necessarily implies calcination under high CO2 partial pressure and fast transitions between carbonation and calcination stages. The multicycle capture performance of the sorbent has been investigated by varying the precalcination time, carbonation/calcination residence times and with the introduction of a recarbonation stage. Results show that the sorbent can be regenerated in very short residence times at 900 °C under high CO2 partial pressure, thus reducing the calciner temperature by about 30–50 °C when compared to limestone. Although the introduction of a recarbonation stage to reactivate the sorbent, as suggested in previous studies for limestone, results in a slightly enhanced capture capacity, the sorbent performance can be significantly improved if the main role of the solid-state diffusion-controlled carbonation is not dismissed. Thus, a notable enhancement of the capture capacity is achieved when the carbonation residence time is prolonged beyond just a few minutes, which suggests a critical effect of solids residence time in the carbonator on the CO2 capture efficiency of the CaL process when integrated into a power plant.

Targeted multifunctional tannic acid nanoparticles

Tannic acid (TA) has multiple effects against cancer, being especially promising in those types that overexpress the epidermal growth factor receptor (EGFR), as TA modulates its activation and downstream signaling pathways, triggering apoptosis. Nonetheless, despite the important role of this receptor in the pathogenesis and progression of a wide variety of tumors, no TA systems targeted to this receptor have been described yet. In this work, we synthesize, characterize by physico-chemical techniques and study the cytotoxic effect and cell uptake of TA nanoparticles targeted to EGFR in both tumoral and normal human skin cells. Our nanoparticles exhibited an extremely high entrapment efficiency, and were only toxic for the tumoral cells. The uptake assay demonstrated that nanoparticles are able to enter the cells through a receptor-mediated mechanism. Furthermore, we have included fluorescent markers in these nanoparticles to combine imaging and therapeutic applications, thus building effectively a multifunctional tool for biomedicine.

The synthesis of nanocrystalline ternary CuInSe2 particles prepared by high-energy milling in a planetary mill in an argon atmosphere from copper, indium and selenium was reported. CuInSe2 particles crystallize in the tetragonal structure with the crystallite size of about 30.5 nm. The Raman spectrum of CuInSe2 nanoparticles shows a strong peak at 176 cm−1 corresponds to the A1 phonon mode of tetragonal CuInSe2 chalcopyrite. HRTEM measurements also revealed the presence of nanocrystals with the size of 10–20 nm with the tendency to form agglomerates. The optical absorption study shows that nanoparticles have direct optical band gap energy of 1.8 eV. The quantum size effect of the particles was confirmed also by PL measurement.

A mechanically induced self-sustaining reaction (MSR) has been successfully employed for manufacturing powdered cermets based on Ti, Ti–Ta and Ti–Nb carbonitrides using Co as the binder phase and Mo2C as the sintering additive. The powders were sintered by hot-pressing, and complete chemical, microstructural and mechanical characterizations were performed on the densified cermets. When elemental Ta, Nb and/or Mo2C were added to the initial raw mixture submitted to the MSR process, smaller ceramic grains were observed after sintering, which suggested that ceramic particle growth was hindered by the presence of Ta, Nb and/or Mo in the host titanium carbonitride structure. Nanoindentation measurements enabled the determination of the hardness of the ceramic and binder phases, and values in the range of 26–29 GPa and 14–16 GPa were found, respectively. The high hardness values of the binder were related to the formation of intermetallic phases.

Effect of dolomite decomposition under CO2 on its multicycle CO2 capture behaviour under calcium looping conditions

One of the major drawbacks that hinder the industrial competitiveness of the calcium looping (CaL) process for CO2 capture is the high temperature (∼930–950 °C) needed in practice to attain full calcination of limestone in a high CO2 partial pressure environment for short residence times as required. In this work, the multicycle CO2 capture performance of dolomite and limestone is analysed under realistic CaL conditions and using a reduced calcination temperature of 900 °C, which would serve to mitigate the energy penalty caused by integration of the CaL process into fossil fuel fired power plants. The results show that the fundamental mechanism of dolomite decomposition under CO2 has a major influence on its superior performance compared to limestone. The inert MgO grains resulting from dolomite decomposition help preserve a nanocrystalline CaO structure wherein carbonation in the solid-state diffusion controlled phase is promoted. The major role played by the dolomite decomposition mechanism under CO2 is clearly demonstrated by the multicycle CaO conversion behaviour observed for samples decomposed at different preheating rates. Limestone decomposition at slow heating rates yields a highly crystalline and poorly reactive CaCO3 structure that requires long periods to fully decarbonate and shows a severely reduced capture capacity in subsequent cycles. On the other hand, the nascent CaCO3 produced after dolomite half-decomposition consists of nanosized crystals with a fast decarbonation kinetics regardless of the preheating rate, thus fully decomposing from the very first cycle at a reduced calcination temperature into a CaO skeleton with enhanced reactivity as compared to limestone derived CaO.

3 mol% Yttria doped zirconia ceramics were consolidated by spark plasma sintering (SPS) at two sintering temperatures with the aim of achieving two different reduction levels. Microstructural characterization of the ceramics was performed by scanning electron microscopy (SEM). Electrical properties were investigated by means of impedance spectroscopy from room temperature up to 500 degrees C. The two ceramics presented a remarkably different electrical behavior. The effect of the extra electrons introduced by reduction during SPS on both the bulk and the grain boundary conductivity was analyzed and discussed.

In this work, Li3xLa2/3-xTiO3 powder with nominal lithium content (x = 0.08) was synthesized by mechano synthesis method. Spark plasma sintering (SPS) was employed to prepare lithium lanthanum titanium oxide solid-state ceramic. The techniques of X-ray diffraction, high resolution scanning electron microscopy, and Raman spectroscopy were used to characterize the composition and microstructure of samples. The results showed that fine-grained ceramics with relative density of 95.5% were obtained by sintering the oxide powders at 1100 degrees C for only 5min.

Effect of lime on stabilization of phyllite clays

This paper represents a new advance in the study of engineering properties and material applications of phyllite clays. Considering their potential use as construction materials for structures subjected to low stress levels, this laboratory research investigated the stabilization and improvement in engineering properties of a Spanish phyllite clay achieved by the addition of 3, 5 and 7 wt.% lime. Geotechnical properties investigated include the consistency limits, compaction, California Bearing Ratio, swelling potential and water-permeability. The phyllite clay–lime mixtures had good compaction properties and very to extremely low permeability-coefficient values, with a semi-logarithmic correlation between increasing permeability and increasing proportion of lime additive. The addition of 3 wt.% lime was sufficient to reach the index of capacity amble specified in the Sheet of Technical General Prescriptions for Works of Roads and Bridges PG–3 (Spanish Highways Agency, 2008), significantly reducing the plasticity index value, with the compacted mixture undergoing no swelling under soakage. The required pavement thicknesses for the raw phyllite–clay material and the phyllite clay–lime mixtures are compared and discussed. Potential applications for phyllite clay–lime mixtures include for pavements/road subgrade, earth construction, building materials and for impermeabilization purposes.

The Structure and Chemical Composition of Wall Paintings From Islamic and Christian Times in the Seville Alcazar

Wall paintings from the Islamic epoch (10th to 12th centuries) and the Christian monarchy (14th to 16th centuries) have been recovered in discarded materials and on walls after reconstruction works in the Seville Alcazar. These paintings have spent centuries underground or under a plaster coat. Portable X-ray fluorescence (XRF) and combined XRF/X-ray diffraction (XRD) were employed in situ, as well as scanning electron microscopy (SEM-EDX), grazing angle incidence XRD and micro-Raman spectroscopy, on cross-section samples to fully characterize the materials in the wall paintings. Using these methods, the fresco technique was demonstrated, and many kinds of pigments were identified in accordance with the various periods of the history of the Alcazar, thus assessing the authenticity of all the wall paintings studied here.

Intensification of hydrogen production by methanol steam reforming

This paper studies the methanol steam reforming intensification to enhance the hydrogen production in a multi-channel block type micro-reformer. The effects of operating parameters such as reforming temperature, space velocity and catalyst layer thickness on reforming performance are investigated. For optimized design and operating conditions, the 8 cm(3) reformer unit produced 170 LH2/h containing on dry basis 75.0% H-2, 23.5% CO2, 0.06% CH3OH and 1.44% CO at 648 K allowing the production of 218-255 Win a commercial PEMFC with 80% hydrogen utilization. This study shows that high methanol conversion can be achieved with high Pd/ZnO catalyst loading at 648 K with very low CO content (<1.5%) in the outlet stream.

Ceramics from clays and by-product from biodiesel production: Processing, properties and microstructural characterization

The production of biodiesel generates a by-product called glycerine which contains glycerol that cannot be reintegrated into the same manufacturing process. The ceramic bricks are an interesting option to set in their structure a wide range of by-products and residues materials and composites, sometimes serving only as a reservoir for the inert residue, and other, having a positive effect on the ceramic material or process. In the present work, the incorporation of this waste in raw clays has been studied. The raw materials: clay and glycerine was characterized by XRD, XRF, CNHS analysis, higher heating value and thermal analysis and after, using conventional moulding and sintering processing methods to prepare clay-glycerine composites, the influence of the amount of waste added to clay has been evaluated. To do this, percentages of glycerine were added to the clay from 5% to 20% and evaluated by a series of technological properties such as compressive strength, absorption and suction of water, bulk density, the study of porosity generated by adsorption-desorption isotherms of N-2, thermal conductivity and finally by the compressive strength after freezing-thaw, it was considered as the maximum permissible rate of addition of glycerol 10-15% in weight, because higher additions have a strong effect on the properties of the obtained materials such as compression strength and bulk density which descending dramatically due to the large amount of porosity generated as reflected by high values of absorption and suction experiments. It was concluded that adding 5% glycerol to the ceramic paste generated plasticity in clay to achieve be moulded, with values of compressive strength of 84 MPa while gets to reduce the density apparent by almost.

Fabrication and characterization of CeO2 pellets for simulation of nuclear fuel

Cerium Oxide, CeO2, has been shown as a surrogate material to understand irradiated Mixed Oxide (MOX) based matrix fuel for nuclear power plants due to its similar structure, chemical and mechanical properties. In this work, CeO2 pellets with controlled porosity have been developed through conventional powder-metallurgy process. Influence of the main processing parameters (binder content, compaction pressure, sintering temperature and sintering time) on porosity and volumetric contraction values has been studied. Microstructure and physical properties of sintered compacts have also been characterized through several techniques. Mechanical properties such as dynamic Young's modulus, hardness and fracture toughness have been determined and connected to powder-metallurgy parameters. Simulation of nuclear fuel after reactor utilization with radial gradient porosity is proposed.

Study by DSC and HRTEM of the aging strengthening of Cu-Ni-Zn-Al alloys

The structural changes of a Cu-12 wt.% Ni-17 wt.% Zn-1.7 wt% Al alloy as a function of the aging temperature have been studied by means of Differential Scanning Calorimetry (DSC), high resolution transmission electron microscopy (HRTEM) and hardness measurements. It has been proposed a hardening mechanism that implies the crystallization of a Ll(0) Cu2NiZn phase coherent with the matrix a phase followed, firstly, by its transformation into a Ll(2) coherent phase and, secondly, by the precipitation of this phase. It has been shown that aluminum play an important role in the precipitation hardening process because Cu2NiZn precipitates are not formed by aging a ternary Cu-Ni-Zn alloy of similar composition. It has been shown by the first time that DSC could be a powerful tool for discriminating the whole set of phase transformations undergone by alloys as a function of the annealing temperature from a single heating run.

Nanocrystalline CuInS2 particles have been synthesized from copper, indium, and sulfur powders by high-energy milling in a planetary mill in an argon atmosphere. Structural characterization of the prepared nanoparticles, including phase identification, Raman spectroscopy, specific surface area measurement, and particle size analysis were performed. The optical properties were studied using UV-Vis absorption and photoluminescence (PL) spectroscopy. The production of CuInS2 (JCPDS 027-0159) particles with a crystallite size of about 17.5-23.5 nm was confirmed by X-ray diffraction. The crystal structure has a tetragonal body-centered symmetry belonging to the I-42d space group. The Raman spectra also proved the formation of pure CuInS2 nanoparticles. TEM and HRTEM measurements revealed the presence of nanoparticles of different dimensions (10-20 nm) and their tendency to form agglomerates. The nanoparticles tend to agglomerate due to their large specific surface area. The average size of the synthesized particles was determined by photon cross-correlation spectroscopy to be in the range of 330-530 nm (bimodal size distribution). The band gap of the CuInS2 particles is 2 eV which is wider than that in bulk materials. The decrease in size leads to the blue-shift of the PL spectra. Therefore, CuInS2 nanoparticles are promising candidates for optical applications, and they have high potential in solar energy conversion.

The Calcium-Looping technology for CO2 capture: On the important roles of energy integration and sorbent behavior

The Calcium Looping (CaL) technology, based on the multicyclic carbonation/calcination of CaO in gas-solid fluidized bed reactors at high temperature, has emerged in the last years as a potentially low cost technology for CO2 capture. In this manuscript a critical review is made on the important roles of energy integration and sorbent behavior in the process efficiency. Firstly, the strategies proposed to reduce the energy demand by internal integration are discussed as well as process modifications aimed at optimizing the overall efficiency by means of external integration. The most important benefit of the high temperature CaL cycles is the possibility of using high temperature streams that could reduce significantly the energy penalty associated to CO2 capture. The application of the CaL technology in precombustion capture systems and energy integration, and the coupling of the CaL technology with other industrial processes are also described. In particular, the CaL technology has a significant potential to be a feasible CO2 capture system for cement plants. A precise knowledge of the multicyclic CO2 capture behavior of the sorbent at the CaL conditions to be expected in practice is of great relevance in order to predict a realistic capture efficiency and energy penalty from process simulations. The second part of this manuscript will be devoted to this issue. Particular emphasis is put on the behavior of natural limestone and dolomite, which would be the only practical choices for the technology to meet its main goal of reducing CO2 capture costs. Under CaL calcination conditions for CO2 capture (necessarily implying high CO2 concentration in the calciner), dolomite seems to be a better alternative to limestone as CaO precursor. The proposed techniques of recarbonation and thermal/mechanical pretreatments to reactivate the sorbent and accelerate calcination will be the final subjects of this review.

Kinetics of high-temperature oxidation of (Ti,Ta)(C,N)-based cermets

The kinetics of the high-temperature oxidation of titanium–tantalum carbonitride-based cermets with different Ti/Ta ratios was studied. Isothermal oxidation tests were conducted under static air for 48 h at temperatures between 700 °C and 1200 °C. The oxidation satisfied the parabolic kinetics, characteristic of the existence of a protective oxide layer. The apparent activation energy suggests the rate-controlling process during oxidation is the simultaneous inward and outward diffusion of oxygen and titanium, respectively, through the formed protective layer, consisting mainly of a rutile phase. A higher Ta(V) content in the rutile decreased the oxygen diffusivity due to the reduction of oxygen vacancy concentration.

High temperature oxidation resistance of (Ti,Ta)(C,N)-based cermets

Cermets based on titanium-tantalum carbonitride were oxidized in static air between 800 degrees C and 1100 degrees C for 48 h. The thermogravimetric and microstructural study showed an outstanding reduction in the oxidation of more than 90% when the Ta content was increased. In cermets with low Ta content, the formation of a thin CoO/Co3O4 outer layer tends to disappear by reacting with the underlying rutile phase, which emerges at the surface. However, in cermets with higher Ta content, the formation of an external titanate layer, observed even at a low temperature, appears to prevent the oxygen diffusion and the oxidation progression.

Influence of tin additions on the precipitation processes in a Cu-Ni-Zn alloys

Influence of tin additions on the precipitation processes in a Cu-Ni-Zn alloys. The influence of 1.1 wt% tin additions on the precipitation hardening of Cu-11 wt% Ni-20 wt% Zn alloy was studied by Differential Scanning Calorimetry (DSC), microhardeness measurements and High Resolution Transmission Electron Microscopy (HRTEM). The calorimetric curves, in the range of temperatures analyzed, show the presence of two exothermic reactions in the ternary alloy, associated to the short-range-order development assisted by migration of excess vacancies. On the other hand, one exothermic and one endothermic reaction are observed in the quaternary alloy, associated to the formation and dissolution of Cu2NiZn precipitates, respectively. It has been show that an addition of 1.1% tin plays an important role in the formation of Cu2NiZn precipitates, responsible for the precipitation hardening of the ternary alloy.

Boron carbide ceramics are the hardest material in Nature after diamond and the cubic phase of boron nitride. Due to this fact, their room-temperature fracture properties are the object of intense research. Paradoxically, high-temperature deformation is essentially unknown, because very high temperatures and stresses are necessarily required and high-quality specimens have not been available until recently. In this paper, the high-temperature compressive creep of fine-grained boron carbide polycrystals is reported. The breakdown of the classical power-law for high-temperature plasticity in ceramics is found. An analytical model is proposed. The model assumes that deformation is produced by dislocation glide. However, since the formation of twins is energetically favorable in this material and they act as strong barriers for dislocation glide, their motion turns to become progressively more difficult as elongation proceeds. The combination of increasing twin barriers and dislocations in mutual interaction is proposed to be the mechanism for high-temperature plasticity in this material. The model is validated with the experimental results. Final elongation of boron carbide specimens is reported to be over 100%, although this material cannot be described as a superplastic ceramic.

Ceramics from the Alcazar Palace in Seville (Spain) dated between the 11th and 15th centuries: Compositions, technological features and degradation processes

For the purpose of chemical characterization, a selection of 29 ceramic fragments from the 11th to 15th century has been made from materials excavated in the Seville Alcazar Palace. The PIXE elemental analysis results indicated that the ceramic bodies can be divided into four groups. The XRD identification of the phases present in the bodies revealed differences in the firing temperatures. The PIXE analysis of the glazes revealed variable PbO and SnO2 contents. The latter component was not detected in all the glazes. Cu, Co, Mn, Fe and Sb elements were associated with green, blue, black and yellow colours, respectively. Some glazes were covered by iridescent layers constituted by lead carbonate and phosphates due to alteration of the glazes. It was also possible to detail the microstructure and composition of the ultimate surface layers responsible for the lustre effect observed in two of the ceramic samples using PIXE and Rutherford backscattering spectrometry (RBS).

This work provides new insights on microstructure and electrical properties of 3 mol% Y2O3-ZrO2 (3YTZP) composites with 0.5, 1, and 1.5 vol% single walled carbon nanotubes (SWNTs). The composites were spark plasma sintered (SPS) in identical conditions at 1250 degrees C from powder prepared by two different processing routines, with the aim of optimizing the SWNTs dispersion throughout the ceramic matrix. High densification and submicrometric grain size were achieved in all the composites. Electrical properties of the composites were characterized in a wide temperature range, and modeling of the impedance properties was approached by means of an equivalent circuit that allows separation of the individual SWNT bundles contribution to resistance from the resistance due to junctions between bundles. Effects of the homogeneous distribution of SWNTs at the ceramic grain boundaries on the crystalline phases, percolation threshold, total conductivity and evolution of junctions' resistivity with temperature were analyzed and discussed.

A new model of the carbonator reactor in the calcium looping technology for post-combustion CO2 capture

The Ca-Looping (CaL) process is considered as a promising technology for CO2 post-combustion capture in power generation plants yielding a minor penalty on plant performance as compared with other capture technologies such as conventional amine-based capture systems. This manuscript presents a new carbonator reactor model based on lab-scale multicyclic CaO conversion results, which take into account realistic CaO regeneration conditions that necessarily involve calcination under high CO2 partial pressure and high temperature. Under these conditions, CaO conversion in the diffusion controlled stage is a relevant contribution to the carbonation degree during typical residence times. The main novelty of the model proposed in the present work is the consideration of the capture efficiency in the diffusion controlled phase of carbonation. It is demonstrated that increasing the residence time by a few minutes in the carbonator yields a significant improvement of the capture efficiency. Model predictions are shown to agree with experimental results retrieved from pilot-scale tests. The new model allows a more accurate evaluation and prediction of carbonator’s performance over a wider range of residence times. The results obtained may be relevant for the optimization of CaL operation parameters to be used in real power plants.

Green pigments of Roman mural paintings from Seville Alcazar

We report here a study of 30 fragments of green wall paintings from Roman times found in the Patio de Banderas excavation in Seville Alcazar. The sample characterisation was realised using optical microscopy, colourimetry, infrared and micro-Raman spectroscopy, X-ray diffraction, and scanning electron microscopy equipped with energy dispersive X-ray spectroscopy. The study of these pigments is important because it can help determine the source or the pictorial technique used. The samples studied in this work have been divided into two groups, according to the composition of their green pigments. In the first group, celadonite has been characterised as the primary component of the green colour; chlorite was also detected. Particles constituted by chromium accompanied by aluminium, iron and zinc were found in all studied samples of this group. Chlorite and chromium oxide could also be responsible for the green colour. The presence of chromium suggested the presence of green colour pigment from Verona. In the second group, a mixture of celadonite and glauconite was detected and could be responsible for the green colour observed. The addition of refracting material such as Egyptian blue was also used. A mixture of Egyptian green and Egyptian blue together with celadonite and glauconite was also found. Four classes of intonaco were recognised and classified based upon the composition of the aggregates.

Ceramics of Bi1-xYxFeO3 solid solutions (x = 0.02, 0.07, and 0.10) have been prepared by mechanical activation followed by sintering. The effect of yttrium content on the structural, electrical, and optical properties of the materials has been studied. Thus, single-phase solid solutions with rhombohedral R3c structure have been achieved for x = 0.02 and 0.07, while for x = 0.10 the main R3c phase has been detected together with a small amount of the orthorhombic Pbnm phase. Multiferroic properties of the samples, studied by differential scanning calorimetry (DSC), showed that both T-N and T-C (temperatures of the antiferromagnetic paramagnetic and ferroelectric-paraelectric transitions, respectively) decrease with increasing yttrium content. The nature of the ferroelectric paraelectric transition has been studied by temperature-dependent X-ray diffraction (XRD), which revealed rhombohedral R3c to orthorhombic Pbnm phase transitions for x = 0.07 and 0.10. On the other hand, for x = 0.02 the high-temperature phase was indexed as Pnma. Optical properties of the samples, as studied by diffuse reflectance spectroscopy, showed low optical band gap that decreases with increasing yttrium content. Prepared ceramics were highly insulating at room temperature and electrically homogeneous, as assayed by impedance spectroscopy, and the conductivity increased with x.

An improved method for determining the external specific surface area and the plasticity index of clayey samples based on a simplified method for non-swelling fine-grained soils

Garzon, E; Sanchez-Soto, PJ
Applied Clay Science, 115 (2015) 97-107

ABSTRACT

Previous studies have used the clay content of soils for estimating the specific surface areas and different correlations have been found, including plasticity-value correlations. Based on several assumptions, Dolinar (2012) proposed a simplified method for determining the external specific surface area of non-swelling fine-grained soils. An equation relates the external specific surface area (BET-nitrogen) with percentage of clay fraction (< 2 μm), determined by hydrometer method, and plasticity index (Atterberg).

In this work, based on that simplified method, the authors have developed an improved method for determining the external specific surface area of fine-grained clay samples. Instead of percentage of clay fraction, it was proposed to use the clay mineral content estimated by XRD methods. From an analysis of previous Dolinars results, the calculated and measured values of external specific surface area were studied for a group of non-swelling and fine-grained soil samples (Dolinar's samples), five non-swelling clayey samples and data samples from the literature. Additionally, an estimation of the plasticity index (Atterberg) has been also considered in this improved method. Both these methods, simplified and improved, were tested and compared using all these samples. It demonstrated the practical application of both these methods for an estimation of external specific surface area and plasticity index. However, in the present research two models were considered to determine the specific surface areas (BET and Langmuir) and the influence of several sources of errors in these predictions was discussed. The predictions were found more accurate when specific surface area from Langmuir's model is considered. It is concluded that the present research will be useful for the prediction of external specific surface area and plasticity index of non-swelling clayey materials and to dispose of theoretical practical relationships between clay mineralogy and geotechnical properties of valuable interest.

Phyllite clays contain clay minerals (chlorite, illite and mixed-layer illite smectite), quartz and feldspars. In this experimental laboratory study, new composites of phyllite clay and cement (5, 7 and 9 wt.%) were prepared and tested to determine their Atterberg limits, dry density and optimum water content for modified Proctor (MP) compaction, California Bearing ratio, swelling potential after soakage in water, unconfined compressive strength (UCS) and water-permeability coefficient. From the mixes investigated, the composite with 5 wt.% cement was deemed most suitable for certain construction material applications, having a plasticity index of 10.5%, maximum dry density of 2.17 Mg/m3 and optimum water content of 8% for MP compaction (undergoing no swelling under soakage), a UCS of 0.74 MPa, and a very low permeability coefficient value of 7.4 × 10− 11 m/s. Potential material applications for these new composites include for building construction, roofs, and flexible pavements.

In this work, a gas flow sputtering (GFS) process which allows the production and deposition of metal nanoparticles (NPs) in a vacuum environment is described. Aim of the study is to prove the potential of this technology for the fabrication of new TiO2 films with enhanced photocatalytic properties. For this purpose, Ag and Pt NPs have been produced and deposited on photocatalytic float glass coated with TiO2 thin films by magnetron sputtering. The influence of the process parameters and of the metal amount on the final properties of the particles (quantity, size, size distribution, oxidation state etc.,) was widely investigated. Moreover, the effect of the NPs on the photocatalytic activity of the resulting materials was evaluated for the case of the decomposition of stearic acid (SA) during UV-A irradiation. The reduction of the water contact angle (WCA) during the irradiation period was measured in order to test the photo-induced super-hydrophilicity (PSH).

High density ceramics of the system Bi1-xLaxFeO3, 0 <= x <= 0.15, have been prepared starting from nanoparticles obtained by mechanosynthesis. The ceramics have been sintered conventionally at 850 degrees C and by spark plasma sintering (SPS). Sintering conditions have been optimized to obtain single phase ceramics, and the microstructure of the ceramics has been compared. Ceramics prepared conventionally present grain sizes from 5 mu m to less than 1 mu m, whereas grain sizes by SPS are in the range from 50 to 100 nm, which demonstrates that it is possible to obtain nanostructured ceramics of La-substituted BiFeO3 using mechanosynthesis followed by SPS at low temperature (625-650 degrees C). The as-prepared SPS ceramics show low resistivity, indicating some reduction in the samples. However, after an oxidative anneal in air, ceramics are highly insulating at room temperature and electrically homogeneous. The high quality of the ceramics has also been demonstrated by XRD, EDX, Raman and DSC.

Fully dense 3 mol% Y2O3-ZrO2 (3YTZP) composites with low single wall carbon nanotube content (0.5, 1 and 1.5 vol% SWNT) were prepared by colloidal processing and spark plasma sintering (SPS). SWNT were distributed at ceramic grain boundaries and also into agglomerates. Characterization of SWNT agglomerates indicated that increase in SWNT vol% does not imply an increase in agglomeration. SWNT agglomerate density was related to the evolution of hardness and fracture toughness with SWNT vol%. Electrical properties of the composites were characterized in a wide temperature range, and percolation threshold was estimated. A model allowing separation of the individual SWNT bundles contribution to resistance from the resistance due to junctions between bundles was proposed for composites with a percolating SWNT network.

Study of coatings by thermal analysis in a monument built with calcarenite

In this research, characterization of materials either added during restoration or formed by environmental contamination in the Seville City Hall, built with calcarenite stone, was investigated by thermal methods. Three different mortars for restoration have been characterized: (a) lime micro-mortar for internal consolidation of mortar itself, (b) mortar for reconstruction of deteriorated areas and (c) mortar with Portland cement. Acrylate polymer as consolidant and protection used was characterized. Addition of gypsum or “white cement” has been also applied in the restoration. Altered materials as black crusts constituted by gypsum, calcite and organic compound were determined by thermal analysis. Patina with high concentration of hydrated calcium oxalate, and the transformation mechanism of calcium oxalate into calcium carbonate and formation of calcium oxide produced by decomposition of the calcite were also characterized in the studied monument by thermal analysis. The patina with hydrated calcium oxalate produced by high biological activity was also studied.

Toughening of complete solid solution cermets by graphite addition

(Ti0.95Ta0.05)(C0.5N0.5)-Co complete solid solution cermets (CSCs) were developed by a mechanochemical synthesis process and a pressureless sintering method. The effect of different percentages of graphite used as a sintering additive on the nature of the binder phase and the mechanical properties of the cermets was investigated. Microstructural and mechanical characterisations were carried out by X-ray diffraction, optical microscopy, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, Vickers hardness, indentation fracture toughness and nanoindentation. The addition of graphite modified the carbon activity during sintering, reducing the dissolution of carbonitride ceramic particles into the molten binder. The amount of Ti and Ta remaining in the binder after sintering gradually decreased as the amount of graphite added increased, which induced a change in the nature of the binder phase. When no graphite was added, the binder consisted of the brittle TixTa1−xCo2 intermetallic phase. With the increase in the amount of graphite added, the formation of more ductile phases, such as TixTa1−xCo3 and α-Co, was observed, causing a significant improvement in the toughness of the cermets.

In Situ Synthesis of a ZrB2-Based Composite Powder Using a Mechanochemical Reaction for the Zircon/Magnesium/Boron Oxide/Graphite System

A ZrSiO4/B2O3/Mg/C system was used to synthesize a ZrB2-based composite through a high-energy ball milling process. As a result of the milling process, a mechanically induced self-sustaining reaction (MSR) was achieved in this system. A composite powder of ZrB2-SiC-ZrC was prepared in situ by a magnesiothermic reduction with an ignition time of approximately 6min. The mechanism for the formation of the product was investigated by studying the relevant subreactions, the stoichiometric amount of B2O3, and thermal analysis.

Morphological changes on graphene nanoplatelets induced during dispersion into an epoxy resin by different methods

A structural analysis demonstrating how the manufacturing method of graphene nanoplatelets (GNPs) into a polymer matrix can strongly modify the GNPs morphology and, consequently, their properties, was carried out. Three different methods based on sonication and high shear forces were used to elucidate defects induction and possible size diminution. Manufacturing methods including high shear forces caused the extension of the GNPs while sonication induces wrinkling of the sheets. Residual stresses are induced in the nanoplatelets structure showing an increase in the Raman intensities ratios I-D/I-G and I-D/I-G when a major cycles number of calendering are applied.

Vanadium carbonitrides (VCxN1-x) were prepared via mechanosynthesis from mixtures of elemental vanadium and carbon with different V/C atomic ratios under a nitrogen atmosphere using a high-energy ball mill. We obtained the full composition range of carbonitrides at room temperature. The products were characterized using X-ray diffraction, scanning electron microscopy and electron energy loss spectroscopy. The results showed particle-sized products with high sinterability and very high microhardness.

Applications of sample-controlled thermal analysis (SCTA) to kinetic analysis and synthesis of materials

The advantages of the sample-controlled thermal analysis (SCTA) for both the kinetic analysis of solid-state reactions and the synthesis of materials are reviewed. This method implies an intelligent control of the temperature by the solid-state reaction under study in such a way that the reaction rate as a function of the time fits a profile previously defined by the user. It has been shown that SCTA has important advantages for discriminating the kinetic model of solid-state reactions as compared with conventional rising temperature methods. Moreover, the advantages of SCTA methods for synthesising materials with controlled texture and structure are analysed.

Valorization and inertization of galvanic sludge waste in clay bricks

Galvanic sludge wastes (GSW) are produced by the physico-chemical treatments of wastewater generated by electroplating plants. These materials have a significant potential for the production of clay ceramic bricks. This paper focuses on the viability of the inertization of heavy metals from GSW mixed with clays. The original materials were obtained by mixing three types of raw clay (red, yellow and black) in equal parts with GSW. These mixtures were characterized by XRD, XRF, and chemical elemental analysis CHNS. The dosage of GSW in the clay–GSW bricks was up to 5 wt.%. The bricks were then manufactured using conventional processes. The influence of the amount of GSW was evaluated after firing the clay–GSW composites at 950 °C for 1 h. The engineering properties of the fired samples, such as density, water absorption, open porosity, water suction and compressive strength, with and without the GSW, were determined. The incorporation of GSW into the clay mix clearly decreased the linear shrinkage and bulk density of the bricks in comparison with the fired clay used as a control. These GSW–clay composites also showed lower open porosity. According to the results obtained for the bulk density of the bricks, samples with GSW addition showed slightly lower values of open porosity than clay bodies, indicating that the GSW–clay samples had slightly higher closed porosity values. This was also shown by SEM. The open porosity, SEM and pore size distribution tests indicated that the porosity generated by the addition of GSW was mainly closed and, therefore, GSW bricks had excellent mechanical properties. The environmental risks of the incorporation of GSW, rich in heavy metals (Cr, Zn, Ni and others), to a clay matrix were evaluated by leaching tests of the fired products. The results indicated a successful inertization of the pollutants.

Nanoindentation of (Ti,Ta)(C,N)-Co cermets prepared by methods of mechanochemistry

Four materials TixTa(1 - x)C(0.5)N(0.5)-20%Co of two chemical compositions (x = 0.9 and 0.95) and two high energy milling methods (one stage and two stage milling) have been prepared. Nano-hardness and elastic modulus for microstructure as a whole and for individual constituent phases (matrix and carbide grains) were obtained by instrumented indentation. Individual targeted indentations as well as grid nanoindentation technique were used to discern the individual constituents' properties. Maximum loads of 20 mN for individual phases and 300 mN for composite microstructure were applied. Materials with higher amount of Ti had larger grains but the milling procedure had stronger influence on the grain size. The two step milling resulted in finer microstructures but with a much wider grain size distribution. Final composite mechanical properties, however, were very similar. Hardness and indentation elasticity modulus of all materials were comparable within the errors of measurement.

Ca-looping for postcombustion CO2 capture: A comparative analysis on the performances of dolomite and limestone

The low cost and wide availability of natural limestone (CaCO3) is at the basis of the industrial competitiveness of the Ca-looping (CaL) technology for postcombustion CO2 capture as already demonstrated by similar to 1 Mw(t) scale pilot projects. A major focus of studies oriented towards further improving the efficiency of the CaL technology is how to prevent the gradual loss of capture capacity of limestone derived CaO as the number of carbonation/calcination cycles is increased. Natural dolomite (MgCa(CO3)(2)) has been proposed as an alternative sorbent precursor to limestone. Yet, carbonation of MgO is not thermodynamically favorable at CaL conditions, which may hinder the capture performance of dolomite. In the work described in this paper we carried out a thermogravimetric analysis on the multicyclic capture performance of natural dolomite under realistic regeneration conditions necessarily implying high calcination temperature, high CO2 concentration and fast transitions between the carbonation and calcination stages. Our study demonstrates that the sorbent derived from dolomite has a greater capture capacity as compared to limestone. SEM analysis shows that MgO grains in the decomposed dolomite are resistant to sintering under severe calcination conditions and segregate from CaO acting as a thermally stable support which mitigates the multicyclic loss of CaO conversion. Moreover, full decomposition of dolomite is achieved at significantly lower calcination temperatures as compared to limestone, which would help improving further the industrial competitiveness of the technology.

Ultra-fast and energy-efficient sintering of ceramics by electric current concentration

Electric current activated/assisted sintering (ECAS) techniques, such as electrical discharge sintering (EDS) or resistive sintering (RS), have been intensively investigated for longer than 50 years. In this work, a novel system including an electrically insulated graphite die for Spark Plasma Sintering (SPS) is described, which allows the sintering of any refractory ceramic material in less than 1 minute starting from room temperature with heating rates higher than 2000°C/min and an energy consumption up to 100 times lower than with SPS. The system alternates or combines direct resistive sintering (DRS) and indirect resistive sintering (IRS). Electrical insulation of the die has been achieved through the insertion of a film made of alumina fibers between the graphite die and the graphite punches, which are protected from the alumina fiber film by a graphite foil. This system localized the electric current directly through the sample (conductive materials) as in DRS and EDS, or through the thin graphite foil (non-conductive materials) as in IRS, and is the first system capable of being used under EDS or RS conditions independently combining current concentration/localization phenomena.

Synthesis of a nanosilica supported CO2 sorbent in a fluidized bed reactor

CaO has been deposited on a nanosilica powder matrix by a procedure based on atomic layer deposition (ALD) in a fluidized bed reactor at atmospheric pressure following a potentially scalable process. In previous works ALD in gas fluidized bed has been mostly performed under reduced pressure, which hampers scaling-up the production technology. The material synthesized in the present work is tested as CO2 solid sorbent at calcium looping conditions. Multicyclic thermogravimetric analysis (TGA) shows that the nanosilica support stabilizes the capture capacity of CaO. EDX-STEM analysis illustrates the presence of Ca well distributed on the surface of the SiO2 nanoparticles.

Influence of the Processing Route on the Carbon Nanotubes Dispersion and Creep Resistance of 3YTZP/SWCNTs Nanocomposites

3YTZP matrix composites containing 2.5 vol% of single-walled carbon nanotubes (SWCNT) were fabricated by Spark Plasma Sintering (SPS) at 1250°C, following different processing routines with the aim of optimizing the SWCNTs dispersion throughout the ceramic matrix. Microstructural characterization of the as-fabricated samples has been performed by means of scanning electron microscopy (SEM). The specimens have been crept at 1200°C to correlate creep resistance and SWCNTs distribution. There are no creep experimental results on these nanocomposites reported in literature. Mechanical results show that the incorporation of SWCNTs into a 3YTZP matrix produces an increase in the strain rate at high temperature with respect to monolithic zirconia. The creep resistance of these nanocomposites decreases with the improvement of the SWCNTs dispersion, where a smaller SWCNTs agglomerate size and consequently a higher concentration of carbon nanotubes surrounding the 3YTZP grain boundaries is found. This fact indicates that SWCNTs act as a lubricant making grain-boundary sliding easier during deformation of these composites.

In this work, we analyze limestone calcination kinetics at environmental conditions involving a CO2 partial pressure P close to the equilibrium pressure Peq by means of in situ X-ray diffraction (XRD) and thermogravimetric (TG) analyses. In contrast with previous empirical observations carried out mostly at conditions far from equilibrium (P/Peq ≪ 1), our results show that the decarbonation rate decreases as the temperature in increased while P/Peq is kept constant, which is explained from a reaction mechanism including desorption of CO2 and the exothermic structural transformation from metastable CaO* nanocrystals to the stable CaO form. The crystal structure and sintering of nascent CaO during calcination has been investigated from in situ XRD analysis, physisorption analysis, and scanning electron microscopy (SEM), which shows that the ratio of the size of polycrystalline CaO grains to crystallite size increases linearly with the CO2 partial pressure in the calcination atmosphere. For high CO2 partial pressures, the size of CaO grains reaches a maximum value of around 1 μm, which leads to a residual surface area of about 1 m2/g, whereas in the limit P → 0 grain size and crystallite size (of the order of 10 nm) would coincide. Accordingly, sintering in the presence of CO2 would be triggered by the agglomeration of CaO crystals enhanced by CO2adsorption, which increases the surface energy. The carbonation reactivity of CaO resulting from calcination scales proportionally to its surface area and is not determined by a growth of the CaO exposed surface along a preferred crystallographic direction wherein carbonation would be unfavorable as suggested in recent works.

New Insights on the Kinetic Analysis of Isothermal Data: The Independence of the Activation Energy from the Assumed Kinetic Model

Isothermal experiments are widely employed to study the kinetics of solid-state reactions or processes to extract essential kinetic information needed for modeling the processes at an industrial scale. The kinetic analysis of isothermal data requires finding or assuming a kinetic function that can properly fit the evolution of the reaction rate with time, so that the resulting parameters, i.e., the activation energy and pre-exponential factor, can be considered reliable. In the present work, we demonstrate using both simulated and experimental data that the kinetic analysis of a set of isothermal plots obtained at different temperatures, considering a single-step solid-state reaction, necessarily leads to the real activation energy, regardless the mathematical function selected for performing the kinetic analysis. This makes irrelevant the election of the kinetic function used to fit the experimental data and greatly facilitates the estimation of the activation energy for any single process.

Role of precalcination and regeneration conditions on postcombustion CO2 capture in the Ca-looping technology

The Ca-looping (CaL) technology is already recognized as a potentially viable method to capture CO2 from postcombustion gas in coal fired power plants. In this process, CO2 is chemisorbed by CaO solid particles derived from precalcination of cheap and widely available natural limestone. The partially carbonated solids are regenerated by calcination under high CO2 concentration. Novel CaL concepts are proposed to further improve the efficiency of the technology such as the introduction of a recarbonation reactor in between the carbonation and calcination stages to mitigate the progressive deactivation of the regenerated CaO. Process simulations aimed at retrieving optimum design parameters and operating conditions to scale-up the technology yield results critically dependent on the multicyclic sorbent performance. Nevertheless, technical limitations usually preclude lab-scale tests from mimicking realistic CaL conditions necessarily involving high CO2 concentration for sorbent regeneration and quick transitions between carbonation and calcination. In this work, a lab-scale experimental analysis is reported on the CaO multicyclic conversion at CaL conditions closely resembling those to be expected in practice. The results presented evidence a relevant role of precalcination conditions. Precalcination in air leads to a strongly adverse effect on the activity of the sorbent regenerated under high CO2 concentration, which is further hindered if a recarbonation stage is introduced. On the other hand, sorbent deactivation is mitigated if precalcination is carried out at conditions similar to those used for sorbent regeneration. In this case, recarbonation helps lessening the loss of multicyclic conversion, which is further enhanced by the synergistic combination with heat pretreatment. Moreover, the present study shows that the kinetics of carbonation is strongly dependent on precalcination and regeneration conditions. The diffusion controlled carbonation phase and recarbonation are intensified if the sorbent is precalcined and regenerated under high CO2 concentration whereas the reaction controlled carbonation phase is notably hampered.

This work focuses on the high-temperature mechanic properties of a 3 mol% yttria zirconia polycrystals (3YTZP), fabricated by hot-pressureless sintering. Systematic measurements of mechanical loss as a function of temperature and frequency were performed. An analytical method, based on the generalized Maxwell rheological model, has been used to analyze the high temperature internal friction background (HTB). This method has been previously applied to intermetallic compounds but never to ceramics, except in a preliminary study performed on fine grain and nanocrystalline zirconia. The HTB increases exponentially and its analysis provides an apparent activation enthalpy which correlates well with that obtained from creep experiments. This fact shows on the one hand the plausibility of applying the generalized Maxwell model to ceramics, and on the other hand indicates the possibility of using mechanical spectroscopy as a complementary helpful technique to investigate the high temperature deformation mechanism of materials.

Dense alumina composites with different carbon nanotube content were prepared by colloidal processing and consolidated by Spark Plasma Sintering (SPS). Single-wall carbon nanotubes (SWNTs) were distributed at grain boundaries and also into agglomerates homogeneously dispersed. Carrying out Vickers hardness tests on the cross-section surfaces instead of top (or bottom) surfaces has shown a noticeable increase in the reliability of the hardness measurements. This improvement has been mainly attributed to the different morphology of carbon nanotube agglomerates, which however does not seem to affect the Vickers hardness value. Composites with lower SWNT content maintain the Vickers hardness of monolithic alumina, whereas it significantly decreases for the rest of compositions. The decreasing trend with increasing SWNT content has been explained by the presence of higher SWNT quantities at grain boundaries. Based on the results obtained, a method for optimizing Vickers hardness tests performance on SWNT/Al2O3 composites sintered by SPS is proposed.

The thermal stability of BiFeO3 prepared by mechanosynthesis and sintered at 850 °C has been studied by DSC as a function of the atmosphere and temperature. It has been found that neither the phase transitions nor the thermal stability of BiFeO3 is affected by the atmosphere in which the heating process is performed. The material is unstable above the α–β transition (TC) and slowly decomposes to produce Bi2O3 and Bi2Fe4O9. The kinetics of this slow process has been studied by performing heating–cooling DSC cycles, concluding it follows an Avrami–Erofeev nucleation and growth kinetic model. The β–γ transition and the peritectic decomposition of BiFeO3 overlap and are kinetically controlled. The kinetics of this complex process has been studied for the first time employing a new kinetic analysis procedure implying the deconvolution and subsequent analysis of the individual contributing stages. Thus, it has been demonstrated that the decomposition of BiFeO3 is accelerated when the sample is heated above the β–γ transition and both processes also follow Avrami–Erofeev kinetic models.

Nanocrystalline Bi2S3 particles have been synthesized from Bi and S powders by high-energy milling in a planetary mill. Structural and microstructural characterization of the prepared particles, including phase identification, specific surface area measurement and particle size analysis has been carried out. The optical properties were measured by spectroscopic methods and the structural stability up to 500 °C was studied by thermal analysis. The production of orthorhombic Bi2S3 with crystallite size of about 26 nm was confirmed by X-ray diffraction. The nanocrystals tend to agglomerate due to their large specific surface area. Accordingly, the average hydrodynamic diameter of the mechanochemically synthesized particles is 198 nm. EDS analysis shows that the synthesized material is pure Bi2S3. The band gap of the Bi2S3 nanoparticles is 4.5 eV which is wider than that in bulk materials. The nanoparticles exhibit good luminescent properties with a peak centered at 490 and 390 nm. Differential scanning calorimetry curves exhibit a broad exothermic peak between 200 and 300 °C, suggesting recovery processes. This interpretation is supported by X-ray diffraction measurements that indicate a 10-fold increase of the crystallite size to about 230 nm. The controlled mechanochemical synthesis of Bi2S3 nanoparticles at ambient temperature and atmospheric pressure remains a great challenge.

The Mitigation Effect of Synthetic Polymers on Initiation Reactivity of CL-20: Physical Models and Chemical Pathways of Thermolysis

In this paper, the thermal decomposition physical models of different CL-20 polymorph crystals and their polymer bonded explosives (PBXs) bonded by polymeric matrices using polyisobutylene (PIB), acrylonitrile butadiene rubber (NBR), styrene butadiene rubber (SBR), Viton A, and Fluorel binders are obtained and used to predict the temperature profiles of constant rate decomposition. The physical models are further supported by the detailed decomposition pathways simulated by a reactive molecular dynamics (ReaxFF-lg) code. It has been shown that both ε-CL-20 and α-CL-20 decompose in the form of γ-CL-20, resulting in close activation energy (169 kJ mol–1) and physical model (first-order autoaccelerated model, AC1). Fluoropolymers could change the decomposition mechanism of ε-CL-20 from the “first-order autocatalytic” model to a “three-dimensional nucleation and growth” model (A3), while the polymer matrices of Formex P1, Semtex, and C4 could change ε-CL-20 decomposition from a single-step process to a multistep one with different activation energies and physical models. Compared to fluoropolymers, PIB, SBR and NBR may make ε-CL-20 undergo more complete N–NO2 scission before collapse of the cage structure. This is likely the main reason why those polymer bases could greatly mitigate the decomposition process of ε-CL-20 from a single step to a multistep, resulting in lower impact sensitivity, whereas fluoropolymers have only a little effect on that. For ε-CL-20 and its PBXs, the impact sensitivity depends not only on the heat built-up period of their decomposition, but also on the probability of hotspot generation (defects in solid crystals and interfaces) especially when it decomposes in a solid state.

Single phase, electrically insulating samples of Bi1−xLaxFeO3 solid solutions have been prepared by mechanosynthesis over the whole compositional range for the first time. Lanthanum substitution influenced the kinetics of the mechanochemical reaction and crystallite size of the products. For 0 ≤ x ≤ 0.15, an increase in the La content produced a significant decrease in the weight-normalized cumulative kinetic energy required to obtain the final product and an increase in the resulting crystallite size. Larger La contents did not affect either the reactivity or the crystallite size. The effect of x on the structure has been identified. Samples in the ranges x ≤ 0.15 and x ≥ 0.45 gave single phase solid solutions with R3c and Pnma space groups, respectively, while for the intermediate range, a non-centrosymetric Pn21a(00γ)s00 super structure was obtained. For 0 ≤ x ≤ 0.30, differential scanning calorimetry showed two endothermic effects corresponding to the Néel temperature (TN, antiferromagnetic–paramagnetic transition) and the Curie temperature (TC, ferroelectric–paraelectric transition), demonstrating their multiferroic character. Compositions with a larger La content only showedTN. Dilatometric and permittivity measurements confirmed the results obtained by DSC for the ferroelectric–paraelectric transition. The composition dependence of TN and TC showed that, at low x, TN < TC, but a cross-over, or isoferroic transition occurred at x [[similar]] 0.28, when TN = TC = 386 °C. Ceramics with 0 ≤ x ≤ 0.15 were highly insulating at room temperature with a resistivity, extrapolated from the Arrhenius plots, of [[similar]] 7 × 1016 to 8 × 1014 Ω cm and an activation energy [[similar]] 1.14–1.20 eV. Magnetization of the samples improved with La substitution.

This work adds new experimental facts on room temperature hardness and flexural strength of alumina and composites with 1, 2, 5 and 10 vol% single-walled carbon nanotubes (SWNT) with similar grain size. Monolithic Al2O3 and composites were spark plasma sintered (SPS) in identical conditions at 1300 A degrees C, achieving high density, submicrometric grain size and a reasonably homogeneous distribution of SWNT along grain boundaries for all compositions with residual agglomerates. Vickers hardness values comparable to monolithic alumina were obtained for composites with low (1 vol%) SWNT content, though they decreased for higher concentrations, attributed to the fact that SWNT constitute a softer phase. Three-point bending flexural strength also decreased with increasing SWNT content. Correlation between experimental results and microstructural analysis by electron microscopy indicates that although SWNT agglomerates have often been blamed for detrimental effects on the mechanical properties of these composites, they are not the main cause for the reported decay in flexural strength.

The dielectric properties of CaCu3Ti4O12 (CCTO) ceramic prepared by mechanochemical synthesis (MCS) were investigated. The effect on dielectric properties of ball-to-powder weight ratio and milling time was investigated and compared to the behavior of CCTO prepared by conventional solid state reaction (CSSR). CCTO ceramic was partially obtained after 6h of the milling process, while complete transformation was obtained during the sintering step of milled powders. It was shown that the dielectric properties of CCTO processed by MCS are dramatically improved compared with samples prepared by CSSR.

Mechanochemically synthesized nanocrystalline Sb2S3 particles

Nanocrystalline Sb2S3 particles have been synthesized from Sb and S powders by high-energy milling in a planetary mill using argon protective atmosphere. X-ray diffraction, particle size analysis, scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, electron diffraction, high resolution transmission electron microscopy, UV-VIS, and differential scanning calorimetry methods for characterization of the prepared particles were applied. The powder X-ray diffraction pattern shows that Sb2S3 nanocrystals belong to the orthorhombic phase with calculated crystallite size of about 36 nm. The nanocrystalline Sb2S3 particles are constituted by randomly distributed crystalline nanodomains (20 nm) and then these particles are forming aggregates. The monomodal distribution of Sb2S3 particles with the average hydrodynamic parameter 210 nm was obtained. The quantification of energy dispersive X-ray spectroscopy analysis peaks give an atomic ratio of 2:3 for Sb:S. The optical band gap determined from the absorption spectrum is 4.9 eV, indicating a considerable blue shift relative to the bulk Sb2S3. Differential scanning calorimetry curves exhibit a broad exothermic peak between 200 and 300°C, suggesting recovery processes. This interpretation is supported by X-ray diffraction measurements that indicate a 23-fold increase of the crystallite size to about 827 nm as a consequence of application of high temperature process. The controlled mechanochemical synthesis of Sb2S3nanoparticles at ambient temperature and atmospheric pressure remains a great challenge.

Calcium-looping for post-combustion CO2 capture. On the adverse effect of sorbent regeneration under CO2

The multicyclic carbonation/calcination (c/c) of CaO solid particles at high temperature is at the basis of the recently emerged Calcium-looping (CaL) technology, which has been shown to be potentially suitable for achieving high and sustainable post-combustion CO2 capture efficiency. Despite the success of pilot plant projects at the MWth scale, a matter of concern for scaling-up the CaL technology to a commercial level (to the GWth scale) is that the CaO carbonation reactivity can be recovered only partially when the sorbent is regenerated by calcination at high temperatures (around 950 °C) as required by the CO2 high concentration in the calciner. In order to reactivate the sorbent, a novel CaL concept has been proposed wherein a recarbonator reactor operated at high temperature/high CO2 concentration leads to further carbonation of the solids before entering into the calciner for regeneration. Multicyclic thermogravimetric analysis (TGA) tests demonstrate the feasibility of recarbonation to reactivate the sorbent regenerated at high calcination temperatures yet at unrealistically low CO2 partial pressure mainly because of technical limitations concerning low heating/cooling rates. We report results from multicyclic c/c and carbonation/recarbonation/calcination (c/r/c) TGA tests at high heating/coling rates and in which the sorbent is regenerated in a dry atmosphere at high CO2 partial pressure. It is shown that at these conditions there is a drastic drop of CaO conversion to a very small residual value in just a few cycles. Moreover, the introduction of a recarbonation stage has actually an adverse effect. Arguably, CaCO3 decomposition in a CO2 rich atmosphere is ruled by CO2 dynamic adsorption/desorption in reactive CaO (1 1 1) surfaces as suggested by theoretical studies, which would preclude the growth of the regenerated CaO crystal structure along these reactive surfaces, and this effect would be intensified by recarbonation. Nevertheless, the presence of H2O in the calciner, which is also adsorbed/desorbed dynamically in CaO reactive planes, would shield CO2 adsorption/desorption thus mitigating the deeply detrimental effect of CO2 on the carbonation reactivity of the regenerated CaO structure. Oxy-combustion, which produces a significant amount of H2O, is currently used in pilot-scale plants to raise the temperature in the calciner. Auxiliary techniques are being explored to help heating the partially carbonated solids since oxyxombustion represents an important penalty to the CaL technology. Our study suggests that steam injection would be necessary in a dry calciner environment to avoid a sharp loss of CaO conversion if the sorbent is regenerated at high CO2 partial pressure.

Relevant Influence of Limestone Crystallinity on CO2 Capture in The Ca-Looping Technology at Realistic Calcination Conditions

We analyze the role of limestone crystallinity on its CO2 capture performance when subjected to carbonation/calcination cycles at conditions mimicking the Ca-looping (CaL) technology for postcombustion CO2 capture. The behavior of raw and pretreated limestones (milled and thermally annealed) is investigated by means of thermogravimetric analysis (TGA) tests under realistic sorbent regeneration conditions, which necessarily involve high CO2 partial pressure in the calciner and quick heating rates. The pretreatments applied lead to contrasting effects on the solid crystal structure and, therefore, on its resistance to solid-state diffusion. Our results show that decarbonation at high CO2 partial pressure is notably promoted by decreasing solid crystallinity. CaO regeneration is fully achieved under high CO2 partial pressure at 900 °C in short residence times for the milled limestone whereas complete regeneration for raw limestone requires a minimum calcination temperature of about 950 °C. Such a reduction of the calcination temperature and the consequent mitigation of multicyclic capture capacity decay would serve to enhance the efficiency of the CaL technology. On the other hand, the results of our study suggest that the use of highly crystalline limestones would be detrimental since excessively high calcination temperatures should be required to attain full decarbonation at realistic conditions.

Scission kinetic model for the prediction of polymer pyrolysis curves from chain structure

There is a significant interest in correlating polymer structure with thermal degradation behavior. Thus, polymer pyrolysis curves could be predicted from the chemical structure of the polymer. Recent proposals correlate the kinetic temperature function directly with the chemical structure of the polymer by means of the dissociation energy while assuming a semi-empirical first order model for the reaction fraction function. However, a first order model lacks physical meaning and produces significant deviations of the predicted curves, mostly under isothermal conditions. Thus, in this work, an upgrade of the method is proposed by using a new random scission kinetic model. The newly proposed kinetic equation has been checked by fitting the experimental data reported by different authors for the thermal pyrolysis of polystyrene. It has been demonstrated that it accounts for the experimental data of polymer degradation under different heating schedules with considerably higher precision than the previously assumed first order kinetics.

Role of crystal structure on CO2 capture by limestone derived CaO subjected to carbonation/recarbonation/calcination cycles at Ca-looping conditions

Large scale pilot plants are currently demonstrating the feasibility of the Calcium-looping (CaL) technology built on the multicyclic calcination/carbonation of natural limestone for post-combustion and precombustion CO2 capture. Yet, limestone derived CaO exhibits a drop of conversion when subjected to multiple carbonation/calcination cycles, which lessens the efficiency of the technology. In this paper we analyze a novel CaL concept recently proposed to mitigate this drawback based on the introduction of an intermediate stage wherein carbonation is intensified at high temperature and high CO2 partial pressure. It is shown that carbonation in this stage is mainly driven by solid-state diffusion, which is determined by the solid's crystal structure. Accordingly, a reduction of crystallinity by ball milling, which favors diffusion, serves to promote recarbonation. Conversely, thermal annealing, which enhances crystallinity, hinders recarbonation. An initial fast phase has been identified in the recarbonation stage along which the rate of carbonation is also a function of the crystal structure indicating a relevant role of surface diffusion. This is consistent with a recently proposed mechanism for nucleation of CaCO3 on the CaO surface in islands with a critical size determined by surface diffusion. A further issue analyzed has been the effects of pretreatment and cycling on the mechanical strength of the material, whose fragility hampers the CaL process efficiency. Particle size distribution of samples dispersed in a liquid and subjected to high energy ultrasonic irradiation indicate that milling promotes friability whereas thermal annealing enhances the resistance of the particles to fragmentation even though pretreatment effects become blurred after cycling. Our study demonstrates that recarbonation conditions and crystal-structure controlled diffusion are important parameters to be considered in order to assess the efficiency of CO2 capture in the novel CaL concept.

Enhanced oxidation resistance of Ti(C,N)-based cermets containing Ta

(TixTa1−x)(C0.5N0.5)–Co-based cermets with various Ta contents (x = 0, 0.01, 0.05, 0.1 and 0.2) were oxidized at 900 °C for 48 h in static air. A parabolic rate law, which is indicative of the formation of a protective oxide layer, was observed for all samples. The multi-layered oxide scale and the internal oxidation region that formed as the oxidation progressed toward the interior of the cermet specimens were characterized using XRD, SEM and EDS. The enhanced oxidation resistance achieved in cermets composed by a hard component with stoichiometry Ti0.95Ta0.05C0.5N0.5 may satisfy the optimal requirements for many applications in the field of cutting tools.

Multicyclic conversion of limestone at Ca-looping conditions: The role of solid-sate diffusion controlled carbonation

Limestone derived CaO conversion when subjected to multiple carbonation/calcination cycles is a subject of interest currently fueled by several industrial applications of the so-called Ca-looping (CaL) technology. The multicyclic CaO conversion at Ca-looping conditions exhibits two main features as demonstrated by thermogravimetric analysis (TGA). On one hand, carbonation occurs by two well differentiated phases: a first kinetically-driven fast phase and a subsequent much slower solid-state diffusion controlled phase. On the other, carbonation in the fast phase usually shows a drastic decay with the cycle number along the first carbonation/calcination cycles. This trend can be reversed by means of heat pretreatment, which induces a marked loss of fast conversion in the first carbonation but enhances diffusion of CO2 in the solid. Upon decarbonation the regenerated CaO skeleton displays an increased conversion in the fast carbonation phase of the next cycle, a phenomenon which has been referred to as reactivation. Nonetheless, sorbent reactivation is hampered by looping carbonation/calcination conditions as those to be likely found in practice such as carbonation stages characterized by low CO2 concentrations and short duration and calcination stages at high temperatures in a CO2 enriched atmosphere, which causes a sintering and loss of activity of the regenerated CaO skeleton. We analyze in this work sorbent reactivation as affected by heat pretreatment and carbonation/calcination conditions. Aimed at shedding light on the role played by these conditions on reactivation we look separately at the multicyclic evolution of conversion in the kinetic and diffusive phases. Generally, the evolution of multicyclic conversion after the first cycle can be described by a balance between the surface area gain due to diffusive carbonation and the surface area loss as caused by sintering in the calcination stage. A significant gain of relative surface area after the first cycle, which is favored by harshening the heat pretreatment conditions, leads however to a marked decay of it during subsequent cycles, which precludes reactivation for an extended interval of cycles. On the other hand, sorbent grinding, if performed before heat pretreatment, leads to a less marked but more sustainable reactivation along the cycles. A novel observation reported in our work is that pretreatment of limestone in a CO2 atmosphere leads upon a subsequent quick decarbonation to a CaO skeleton with extraordinarily enhanced reactivity in the kinetically-driven carbonation phase and with a high resistance to solid-state diffusion, which can be attributed to annealing of the crystal structure as reported by independent studies.

Processing and characterisation of cermet/hardmetal laminates with strong interfaces

Cemented carbides and cermets are potential materials for high speed machining tools. However, cemented carbides are not chemically stable at high temperature and cermets present poor fracture toughness. Novel cermet/hardmetal multilayer systems show a huge potential for this intended application. It would be possible to achieve the right balance of the required thermomechanical properties using cermet as temperature protective outer layers and hardmetal as reinforcement layers. In this work, preliminary results on the microstructural and mechanical characterisation of a multilayer TiCxN1−x–Co/WC–Co composite densified by hot pressing are presented, with special attention to the properties of the interface. Microstructural observations revealed the existence of strong bonding interfaces between cermet and hardmetal layers due to chemical interaction during the sintering process. As a consequence, owing to the different coefficient of thermal expansion between cermet and hardmetal, a tensile and compressive biaxial residual stress of σres,Cermet ≈ +260 ± 50 MPa and σres,WC–Co ≈ −350 ± 70 MPa was estimated in the corresponding layers. Microindentation cracks introduced in the cermet layers (the less toughness material) and propagated transversely to the layers were arrested at the interface, showing the combined effect of toughness and compressive stresses on crack shielding.

Improvement of the thermal stability of branched poly(lactic acid) obtained by reactive extrusion

One-step reactive extrusion-calendering process (REX-calendering) has been used in order to obtain sheets of 1 mm from poly(lactic acid) modified with a styrene-acrylic multifunctional oligomeric agent. In a preliminary internal mixer study, torque versus time has been monitored in order to ascertain chain extender ratios and reaction time. Once all the parameters were optimized, reactive extrusion experiments have been performed. An enhanced general analytical equation has been developed in order to evaluate the kinetic parameters of the thermal degradation of PLA sheets manufactured by reactive extrusion. This improvement has consisted of replacing the n-order conversion function by a modified form of the Sestak–Berggren equation f(α) = c (1 − α)nαm that led to a better adjustment of experimental data and also adequately represented the conventional mechanisms for solid-state processes. The kinetic parameters so obtained have been compared to those determined by conventional differential methods and n-order reaction kinetics. Given that the thermal degradation of PLA has been argued to be caused by random chain scission reactions of ester groups, the conversion function f(α) = 2 (α1/2 − α), corresponding to a random scission mechanism for L = 2 (as well as other functions for L values up to 8), has been tested. Once optimized the kinetic model, the thermal degradation kinetics of sheets obtained by REX-calendering process was compared to that of conventional sheets and polymer matrix.

The role of boron oxide and carbon amounts in the mechanosynthesis of ZrB2–SiC–ZrC nanocomposite via a self-sustaining reaction in the zircon/magnesium/boron oxide/graphite system

Herein, ZrSiO4/B2O3/Mg/C system was used to synthesize a ZrB2-based composite by means of a high energy ball milling process. A mechanically induced self-sustaining reaction was achieved in this system. A nanocomposite powder of ZrB2–SiC–ZrC was prepared with an ignition time of approximately 6 min of milling. The role of the stoichiometric amounts of B2O3 and carbon was investigated to clarify the governing mechanism for the formation of the product.

Effect of high SWNT content on the room temperature mechanical properties of fully dense 3YTZP/SWNT composites

This paper is devoted to correlate the microstructure and room temperature mechanical properties of single-wall carbon nanotube (SWNT) reinforced 3 mol% yttria stabilized tetragonal zirconia with high SWNT content (2.5, 5 and 10 vol%). Fully dense composites were prepared by using a combination of aqueous colloidal powder processing and Spark Plasma Sintering. SWNTs were located at the ceramic grain boundaries and they were not damaged during the sintering process. The weak interfacial bonding between SWNTs and ceramic grains together with the detachment of SWNTs within thick bundles have been pointed out as responsible for the decrease of hardness and fracture toughness of the composites in comparison with the monolithic 3YTZP ceramic.

Effect of Heat Pretreatment/Recarbonation in the Ca-Looping Process at Realistic Calcination Conditions

Even though an increasing number of pilot-scale plants are demonstrating the potential efficiency of the Ca-looping technology to capture CO2 at a commercial level, a still standing matter of concern is the loss of carbonation reactivity of the regenerated CaO by calcination, which is expected to be particularly marked at realistic conditions necessarily implying a high CO2 partial pressure in the calciner. In this work, we address the effect of previously reported strategies for sorbent reactivation, namely heat pretreatment and the introduction of a recarbonation stage before regeneration. Both techniques, either combined or separately, are shown to favor the carbonation reactivity, albeit CaO regeneration is usually carried out at low CO2 partial pressure in lab-scale tests. Novel results reported in this paper show the opposite when the sorbent is regenerated by calcination at high CO2 concentration, which is arguably due to the diverse mechanisms that rule decarbonation depending on the CO2 concentration in the calciner atmosphere. Dynamic and reversible adsorption/desorption of CO2 is thought to govern decarbonation during calcination at high CO2 partial pressure, which would be hindered by the introduction of a recarbonation stage before carbonation. Moreover, carbonation in the fast phase is severely hampered as a result of the marked loss of reactivity of the surface of CaO regenerated under high CO2 partial pressure. On the other hand, heat pretreatment and harsh calcination conditions lead to a notable enhancement of diffusion, which would favor the process efficiency. In these conditions, diffusion controlled carbonation becomes a significant contribution to CaO conversion, which is notably increased by prolonging the carbonation stage. Heat pretreatment allows also reducing the calcination temperature at high CO2 partial pressure while still achieving full decarbonation in short residence times.

Cex Zr1−x O2 (x = 0.10, 0.16 and 0.33) nanocrystalline powders were obtained by a two-step synthesis technique and sintered by spark plasma sintering (SPS). As consequence of the reduction of Ce4+ to Ce3+ species by carbon in the graphite environment in SPS, phase assemblies including tetragonal, monoclinic and pyrochlore phases were generated in the ceramics during the sintering process. The electrical conductivity was highly dependent on phase assembly and atmosphere (N2, H2 and O2). A significant decrease in the activation energy was noticed in the ceramics with high pyrochlore content when measuring the conductivity in H2 atmosphere, consequence of the strong reduction promoted in these ceramics during the measurement. Equal conduction behavior with similar activation energy was observed in all the ceramics when measuring in O2 atmosphere.

Materials characteristics of Roman and Arabic mortars and stuccoes from The Patio de Banderas in the Real Alcazar of Seville (SPAIN)

Garofano, I; Robador, MD; Duran, A
Archaeometry, 56 (2014) 541-561

ABSTRACT

This study discusses the materials and traditional knowledge used in the manufacture and application of lime mortars and stuccoes by Romans and Arabs in Seville (southern Iberian Peninsula). All of the samples studied contain calcite as a binder, combined with aggregates based on river sand from the filling materials of the Guadalquivir River's depression, located in the vicinity of the Real Alcazar Palace in Seville, Spain, where the artefacts were discovered. The Romans used high-quality production technology, as evidenced by the careful selection of raw materials as well as by the adequate binder-to-aggregate ratio and the elevated homogeneity of the mortars and stuccoes. The suitable distribution of aggregates resulted in higher density values for Roman fragments than for Arabic ones. Results derived from Arabic samples suggest a decline in technology manufacture over time. This work provides useful information, particularly regarding the Roman and Arabic periods in the Iberian Peninsula. The analytical techniques employed in this study were X-ray diffraction (XRD), X-ray fluorescence (XRF)—using conventional and portable systems, scanning electron microscopy (SEM), petrographic microscopy, differential thermal analysis/thermogravimetry (DTA/TG), particle-size analysis and mercury intrusion porosimetry.

High and stable CO2 capture capacity of natural limestone at Ca-looping conditions by heat pretreatment and recarbonation synergy

The Ca-looping (CaL) process, based on the multicyclic carbonation/calcination of limestone derived CaO, has emerged recently as a potentially economically advantageous technology to achieve sustainable postcombustion and precombustion CO2 capture efficiencies. Yet, a drawback that hinders the efficiency of the CaL process is the drastic drop of limestone capture capacity as the number of carbonation/calcination cycles is increased. Precalcination of limestone at high temperatures for a prolonged period of time has been proposed as a potential technique to reactivate the sorbent, which is however precluded by regeneration temperatures above 850 degrees C and low CO2 concentrations in the carbonator to be found in the practical situation. Under these conditions, heat pretreatment leads to a stable yet very small CaO conversion. On the other hand, the introduction of a recarbonation stage between the ordinary carbonation and calcination stages has been shown to decelerate the rate of sorbent activity decay even though this favorable effect is not noticeable up to a number of above 10-15 cycles. The present manuscript demonstrates that the synergetic action of heat pretreatment and recarbonation yields a high and stable value for the multicyclic conversion of limestone derived CaO. It is foreseen that recarbonation of heat pretreated limestone would lead to a reduction of process costs especially in the case of precombustion applications. Even though sorbent purging will always be needed because of ash accumulation and sul-phation in postcombustion CO2 capture applications, the stable and high multicyclic CaO conversion achieved by the combination of these techniques would make it necessary to a lesser extent.

Chemical and electrical properties of LSM cathodes prepared by mechanosynthesis

Mechanosynthesis of La1−xSrxMnO3 (x = 0, 0.25, 0.5, 0.75 and 1) was carried out at room temperature from stoichiometric mixtures of La2O3, Mn2O3 and SrO, obtaining monophasic powders with the perovskite structure. Physical properties of these materials and their chemical compatibility with the electrolyte yttria stabilized zirconia (YSZ), which depend strongly on the La/Sr ratio, were evaluated to corroborate availability to be implemented as cathode material in solid oxide fuel cells (SOFCs). Electrical conductivity values in air ranged between 100 and 400 S cm−1 in the temperature range of 25–850 °C. Samples presented low reactivity with YSZ in the working temperature range (600–1000 °C) maintaining the grain size small enough to preserve the catalytic activity for oxygen reduction.

This work presents a CO2 sorbent that may be synthesized from low-cost and widely available materials following a simple method basically consisting of impregnation of a nanostructured silica support with a saturated solution of calcium nitrate. In a first impregnation stage, the use of a stoichiometric CaO/SiO2 ratio serves to produce a calcium silicate matrix after calcination. This calcium silicate matrix acts as a thermally stable and mechanically hard support for CaO deposited on it by further impregnation. The CaO-impregnated sorbent exhibits a stable CaO conversion at Ca-looping conditions whose value depends on the CaO wt% deposited on the calcium silicate matrix, which can be increased by successive reimpregnations. A 10 wt% CaO impregnated sorbent reaches a stable conversion above 0.6 whereas the stable conversion of a 30 wt% CaO impregnated sorbent is around 0.3, which is much larger than the residual conversion of CaO derived from natural limestone (between 0.07 and 0.08). Moreover, particle size distribution measurements of samples predispersed in a liquid and subjected to high energy ultrasonic waves indicate that the CaO-impregnated sorbent has a relatively high mechanical strength as compared to limestone derived CaO.

The effect of polymer matrices on the thermal hazard properties of RDX-based PBXs by using model-free and combined kinetic analysis

In this paper, the decomposition reaction models and thermal hazard properties of 1,3,5-trinitro-1,3,5-triazinane (RDX) and its PBXs bonded by Formex P1, Semtex 1A, C4, Viton A and Fluorel polymer matrices have been investigated based on isoconversional and combined kinetic analysis methods. The established kinetic triplets are used to predict the constant decomposition rate temperature profiles, the critical radius for thermal explosion and isothermal behavior at a temperature of 82 C. It has been found that the effect of the polymer matrices on the decomposition mechanism of RDX is significant resulting in very different reaction models. The Formex P1, Semtex and C4 could make decomposition process of RDX follow a phase boundary controlled reaction mechanism, whereas the Viton A and Fluorel make its reaction model shifts to a two dimensional Avrami-Erofeev nucleation and growth model. According to isothermal simulations, the threshold cook-off time until loss of functionality at 82 degrees C for RDX-C4 and RDX-FM is less than 500 days, while it is more than 700 days for the others. Unlike simulated isothermal curves, when considering the charge properties and heat of decomposition, RDX-FM and RDX-C4 are better than RDX-SE in storage safety at arbitrary surrounding temperature.

Understanding the Role of the Cosolvent in the Zeolite Template Function of Imidazolium-Based Ionic Liquid

In this work, a study for understanding the role played by [ClBmim], [BF4Bmim], [PF6Bmim], and [CH3SO3Bmim] ionic liquids (ILs) in the synthesis of zeolites is presented. The use of [ClBmim] and [CH3SO3Bmim] ILs, as reported earlier [ Chem. Eur. J. 2013, 19, 2122] led to the formation of MFI or BEA type zeolites. Contrary, [BF4Bmim] and [PF6Bmim] ILs did not succeed in organizing the Si–Al network into a zeolite structure. To try to explain these results, a series of quantum mechanical calculations considering monomers ([XBmim]) and dimers ([XBmim]2) by themselves and plus cosolvent (water or ethanol) were carried out, where X ≡ Cl–, BF4–, PF6–, or CH3SO3–. Our attention was focused on the similarities and differences among the two types of cosolvents and the relation between the structure and the multiple factors defining the interactions among the ILs and the cosolvent. Although a specific pattern based on local structures explaining the different behavior of these ILs as a zeolite structuring template was not found, the calculated interaction energies involving the Cl– and CH3SO3– anions were very close and larger than those for BF4– and PF6– species. These differences in energy can be used as an argument to describe their different behavior as structure directing agents. Moreover, the topology of the cosolvent is also an ingredient to take into account for a proper understanding of the results.

The synthesis of (Ti1 − xZrx)B2–Al2O3, (Ti1 − xHfx)B2–Al2O3 and (Zr1 − xHfx)B2–Al2O3 (x = 0, 0.5 and 1) powder nanocomposites via a mechanochemical method using TiO2, ZrO2, HfO2, HBO2 and Al as the raw materials was investigated. The formation of the nanocomposites proceeds via a mechanically-induced self-sustaining reaction (MSR) process that involves several simultaneous reactions. The aluminothermic reductions of the TMO2 and HBO2 produce Al2O3 and transition metal and boron elements, which in turn react to yield the diboride phase. The ignition of the complex combustion reaction occurred after a short milling time (15–30 min), instantly transforming most of the reactants into products. The sample composition was marked by the stoichiometry of the combustion reaction, and the resulting nanocomposites were analysed using XRD, ED, SEM, TEM and EDX techniques. The X-ray results confirmed the biphasic character of the prepared composite powder (TMB2 and Al2O3 structures); minor amounts of the Zr and Hf oxides were also observed. The achieved microstructure was characterised by the agglomeration of Al2O3 nanocrystallites and diboride crystals with a diffraction domain size ranging between 100 and 300 nm.

Comparison of thermal behavior of natural and hot-washed sisal fibers based on their main components: Cellulose, xylan and lignin. TG-FTIR analysis of volatile products

This paper presents in a comprehensive way the thermal behavior of natural and hot-washed sisal fibers, based on the fundamental components of lignocellulosic materials: cellulose, xylan and lignin. The research highlights the influence exerted on the thermal stability of sisal fibers by other constituents such as non-cellulosic polysaccharides (NCP) and mineral matter.

Thermal changes were investigated by thermal X-ray diffraction (TXRD), analyzing the crystallinity index (%Ic) of cellulosic samples, and by simultaneous thermogravimetric and differential thermal analysis coupled with Fourier-transformed infrared spectrometry (TG/DTA-FTIR), which allowed to examine the evolution of the main volatile compounds evolved during the degradation under inert and oxidizing atmospheres. The work demonstrates the potential of this technique to elucidate different steps during the thermal decomposition of sisal, providing extensible results to other lignocellulosic fibers, through the analysis of the evolution of CO2, CO, H2O, CH4, acetic acid, formic acid, methanol, formaldehyde and 2-butanone, and comparing it with the volatile products from pyrolysis of the biomass components. The hydroxyacetaldehyde detected during pyrolysis of sisal is indicative of an alternative route to that of levoglucosan, generated during cellulose pyrolysis.

Hot-washing at 75 °C mostly extracts non-cellulosic components of low decomposition temperature, and reduces the range of temperature in which sisal decomposition occurs, causing a retard in the pyrolysis stage and increasing TbNCP and TbCEL, temperatures at the maximum mass loss rate of non-cellulosic polysaccharides and cellulose decompositions, respectively. However, enriching sisal fibers in cellulose produces a decrease of TbCEL under an oxidizing atmosphere, and furthermore, a delay of the combustion process, displacing TbCOM to higher temperatures.

The results and findings of the paper would help further understanding of thermal processes where Agave fibers are involved, as the decomposition of their composites.

Analysis on the mechanical strength of WC-Co cemented carbides under uniaxial and biaxial bending

The mechanical strength of three WC-Co grades was determined and compared under uniaxial and biaxial bending. Uniaxial four-point bending was conducted on bar-shaped specimens; biaxial testing was performed on discs using the ball-on-three-balls (B3B) method. Strength results were analysed within the frame of the Weibull theory. Differences in characteristic strength between uniaxial and biaxial bending were explained as an effect of the effective surface tested in each case. A higher Weibull modulus was obtained in one grade, independent of the testing method, which was related to its higher fracture toughness. The use and validity of the B3B biaxial test to determine the strength distribution of cemented carbides is discussed.

Enhanced general analytical equation for the kinetics of the thermal degradation of poly(lactic acid)/montmorillonite nanocomposites driven by random scission

An enhanced general analytical equation has been developed in order to evaluate the kinetic parameters of the thermal degradation of nanocomposites, composed of poly(lactic acid) (PLA) and organo-modified montmorillonite (OMMT) nanoparticles. This improvement has consisted of replacing the n-order conversion function by a modified form of the Sestak–Berggren equation f(α) = c (1 − α)nαm that led to a better adjustment of experimental data and also adequately represented the conventional mechanisms for solid-state processes. The kinetic parameters so obtained have been compared to those determined by conventional differential and isoconversional methods. Given that the thermal degradation of PLA has been argued to be caused by random chain scission reactions of ester groups, the conversion function f(α) = L (L − 1)x(1 − x)L−1, corresponding to a random scission mechanism, has been tested. Once optimized the kinetic model, the thermal degradation kinetics of nanocomposites (0.5 and 2.5% of OMMT) was compared to that of the polymer matrix. Moreover, the thermal stability of nanocomposites was tested and compared to that of the polymer matrix.

An investigation on the formation mechanism of nano ZrB2 powder by a magnesiothermic reaction

Nanocrystalline zirconium diboride (ZrB2) powder was produced by mechanochemistry from the magnesiothermic reduction in the Mg/ZrO2/B2O3 system. The use of high-energy milling conditions was essential to induce a mechanically induced self-sustaining reaction (MSR) and significantly reduce the milling time required for complete conversion. Under these conditions, it was found that the ignition time for ZrB2 formation was only about a few minutes. In this study, the mechanism for the formation of ZrB2 in this system was determined by studying the relevant sub-reactions, the effect of stoichiometry, and the thermal behavior of the system.

A unique combination of high-energy ball-milling, annealing, and spark-plasma sintering has been used to process superhard B4C ceramics with ultrafine-grained, dense microstructures from commercially available powders, without sintering additives. It was found that the ultrafine powder prepared by high-energy ball-milling is hardly at all sinterable, but that B2O3 removal by gentle annealing in Ar provides the desired sinterability. A parametric study was also conducted to elucidate the role of the temperature (1600–1800 °C), time (1–9 min), and heating ramp (100 or 200 °C/min) in the densification and grain growth, and thus to identify optimal spark-plasma sintering conditions (i.e., 1700 °C for 3 min with 100 °C/min) to densify completely (>98.5%) the B4C ceramics with retention of ultrafine grains (∼370 nm). Super-high hardness of ∼38 GPa without relevant loss of toughness (∼3 MPa m1/2) was thus achieved, attributable to the smaller grain size and to the transgranular fracture mode of the B4C ceramics.

Mineralogical Characterization of the Polychrome in Cultural Heritage Artifacts (Antiquity to Date) from Southern Spain Using Micro-Raman Spectroscopy and Complementary Techniques

This work reports on the use of micro-Raman spectroscopy for the characterization of materials used for producing the polychrome in cultural heritage artifacts from southern Spain. The micro-Raman technique was applied for the characterization of several types of artworks or for cross-sections from these works, which were produced along different historical epochs. This technique was demonstrated to be valuable for the characterization of compounds, which were all detected within the artworks studied. The identification of all of these compounds by micro-Raman was confirmed by other complementary techniques, such as micro-X-ray diffraction and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy.

Mesoporous gamma alumina fibres of high surface area, stable up to 1000 °C, were synthesized by bioreplica technique using sisal fibres as templates. Alumina formation during pyrolysis and calcination of fibres infiltrated with aluminium chloride solution has been studied, paying special attention to the interaction between the precursor and sisal fibres, using several experimental techniques such as ATR-FTIR, coupled TG-FTIR and thermo-XRD analysis. The morphology and microstructure of the resulting alumina fibres were characterized using SEM and TEM. The crystallographic analysis of the alumina sample performed by electron and X-ray diffraction suggests that fibres are constituted by η and γ-Al2O3 crystallites, whose chemical structure was confirmed by ATR-FTIR and Al27-MAS-NMR. The specific surface area and porosity of ceramic fibres were determined by N2 and CO2 adsorption–desorption measurements. Resulting alumina fibres retain high specific surface areas of 200 and 150 m2/g even after calcination at 1000 °C for 15 h in dry air and for 4 h in wet air, respectively.

Spinodal decomposition and precipitation in Cu–Cr nanocomposite

In this study, spinodal decomposition and precipitation mechanism of mechanically alloyed supersaturated Cu–3wt.%Cr and Cu–5wt.%Cr solid solutions was investigated under nonisothermal aging. Decomposition mechanism and kinetics were studied using differential scanning calorimetry (DSC) and X-ray diffraction (XRD) techniques. Also, the microstructure was characterized by transmission electron microscopy (TEM). Effect of Al2O3 reinforcement on the aging kinetics was also evaluated. It was found that Cu–3wt.%Cr and Cu–5wt.%Cr solid solutions undergo spinodal decomposition at initial stages of ageing. However, decomposition mechanism was changed to nucleation and growth by the aging progress. The aging kinetics for the Cu–Cr/Al2O3 composition appeared to be slightly faster than that for Cu–Cr, since the ageing activation energy is decreased in presence of Al2O3 nano-particles. This behavior is probably due to the higher dislocation density and other structural defects previously produced during ball milling. A detailed comparison of the DSC results with those obtained by TEM, showing good consistency, has been presented. The average size of Cr-rich precipitates was about 10 nm in the copper matrix.

Wall paintings studied using Raman spectroscopy: A comparative study between various assays of cross sections and external layers

This work describes a comparative study between in situ applications of portable Raman spectroscopy and direct laboratory measurements using micro-Raman spectroscopy on the surface of small samples and of cross sections. The study was performed using wall paintings from different sites of the Alcazar of Seville.

Little information was obtained using a portable Raman spectrometer due to the presence of an acrylic polymer, calcium oxalate, calcite and gypsum that was formed or deposited on the surface. The pigments responsible for different colours, except cinnabar, were not detected by the micro-Raman spectroscopy study of the surface of small samples taken from the wall paintings due to the presence of surface contaminants.

The pigments and plaster were characterised using cross sections. The black colour consisted of carbon black. The red layers were formed by cinnabar and white lead or by iron oxides. The green and white colours were composed of green emerald or atacamite and calcite, respectively. Pb3O4 has also been characterised. The white layers (plaster) located under the colour layers consisted of calcite, quartz and feldspars. The fresco technique was used to create the wall paintings.

A wall painting located on a gypsum layer was also studied. The Naples yellow in this wall painting was not characterised due to the presence of glue and oils.

This study showed the advantage of studying cross sections to completely characterise the pigments and plaster in the studied wall paintings.

Study and restoration of the Seville City Hall facade

Before restoring the Seville City Hall façade, a study of the original materials and the compounds added or formed was performed. The stone is fine-grained carbonate rock. Gypsum and mortars were used to restore stone fragments. A black crust was also found the wall was covered with an acrylic resin. A layer of lime on the surface was also detected. The restoration was intended to preserve the artistic quality and uniqueness of this building. The cleaning, reinforcing and innovatively consolidating and protecting the stone using suitable materials similar to those used in the original construction are described in this study.

Effect of tantalum content on the microstructure and mechanical behavior of cermets based on (TixTa1−x)(C0.5N0.5) solid solutions

Titanium–tantalum carbonitride, (Ti, Ta)(C, N), based cermets with different Ti and Ta contents were prepared using a mechanically induced self-sustaining reaction and then densified using a pressureless sintering process. Complete microstructural and mechanical characterizations were performed on the materials, which revealed that the size of the carbonitride ceramic particle was significantly reduced when the Ta content was increased. The flexural strength and fracture toughness were measured using the ball on three balls test and the indentation microfracture test, respectively. The strength profile was analyzed under the framework of Weibull theory. The change in the mechanical properties as a function of the Ta content was correlated with the normalized microstructural parameters, such as the binder mean free path. The decrease in toughness and flexural strength was attributed to the presence of intermetallic compounds in the binder phase, which was also corroborated by the nanoindentation tests.

CdSe@ZnS nanocomposites prepared by a mechanochemical route: No release of Cd2+ ions and negligible in vitro cytotoxicity

CdSe@ZnS nanocomposites have been prepared by a two-step solid state mechanochemical synthesis. CdSe prepared from Cd and Se elements in the first step was mixed with zinc acetate and sodium sulphide in the second step of milling to prepare a CdSe@ZnS nanocomposite. In the third step, the obtained nanocomposite was coated with l-cysteine to prepare a biocompatible system. The crystallite size of the new type of nanocomposite was 20–35 nm for cubic CdSe and 3–8 nm for hexagonal ZnS as calculated from XRD, TEM and SEM data. The synthesised samples show good crystallinity and have been tested for dissolution and cytotoxicity. The dissolution of cadmium from CdSe@ZnS was less than 0.05 μg mL−1, whereas a value of 0.8 μg mL−1 was measured for CdSe alone. The binding of ZnS with CdSe in the nanocomposite practically eliminated the release of cadmium into solution. As a consequence, a very low cytotoxic activity has been evidenced for CdSe@ZnS. The nanocomposites coated with l-cysteine have a great potential as fluorescent labels in biomedical engineering.

Aluminium and magnesium were used in the M/ZrSiO4/B2O3/C (M = Al, Mg) system to induce a mechanically induced self-sustaining reaction (MSR). Aluminium was not able to reduce the system to the desired products, and the system became amorphous after 10 h milling. However, nanocomposite powder of ZrB2–SiC–ZrC was in situ synthesized by the magnesiothermic reduction with an ignition time of approximately 6 min. The mechanism for the formation of the product in this system was determined by studying the relevant sub-reactions.

Eggshell membrane and lead acetate were successfully used as precursors for the mechanochemical synthesis of lead sulphide nanocrystals with crystallite sizes ∼8 nm. XRD, specific surface area measurements, SEM and EDX were used to characterise the synthesised material. The mechanochemical synthesis follows three-step mechanism. The “fish-like” grains with sizes around 30 μm were obtained.

Arsenic sorption by nanocrystalline magnetite: An example of environmentally promising interface with geosphere

In this paper, the sorption of arsenic onto nanocrystalline magnetite mineral Fe3O4 was studied in a model system. Nanocrystalline magnetite was produced by mechanical activation in a planetary ball mill from natural microcrystalline magnetite. As a consequence of milling, the specific surface area increased from 0.1 m2/g to 11.9 m2/g and the surface site concentration enhanced from 2.2 sites/nm2 to 8.4 sites/nm2. These changes in surface properties of magnetite lead to the enhancement of arsenic removal from model system. The best sorption ability was achieved with magnetite sample activated for 90 min. In this case the sample was able to absorb around 4 mg/g. The structural changes of magnetite were also observed and the new hematite phase was detected after 120 min of milling. A good correlation between the decreasing particle size, increasing specific surface area and reduction of saturation magnetization was found. In desorption study, KOH and NaOH were found as the best eluents where more than 70% of arsenic was released back into the solution. The principal novelty of the paper is that mineral magnetite, truly one nature's gift can be used after “smart” milling (mechanical activation) as an effective arsenic sorbent.

Monomeric Ni and Pd hydroxides stabilized by the iPrPCP pincer ligand react with CO2 to give labile terminal bicarbonate complexes that readily lose CO2 and water to give binuclear carbonate complexes. Differential scanning calorimetry (DSC) has been used to monitor the decomposition of both bicarcabonates in the solid state. When the carbonate complexes are heated under reflux in thf in the presence of water, full decarboxylation takes place, restoring the starting hydroxides and demonstrating that CO2 insertion is a fully reversible process. The decarboxylation of the nickel carbonate complex is completed more readily, suggesting that the reaction of the Pd hydroxide with CO2 is more favourable than that of its nickel counterpart. This is supported by DFT calculations, which also shows that CO2 insertion takes place through a concerted Lipscomb-type mechanism. Monomeric Ni and Pd hydroxides stabilized by the iPrPCP pincer ligand react with CO2 to give labile terminal hydrogen carbonate complexes that readily lose CO2 and water to give binuclear carbonate complexes.

ZrB2–Al2O3 nanocomposite powder was produced by aluminothermic reduction in Al/ZrO2/B2O3 system. In this research, high energy ball milling was used to produce the necessary conditions to induce a mechanically induced self-sustaining reaction. The ignition time of the composite formation was found to be about 13 min. The synthesis mechanism in this system was investigated by examining the corresponding sub-reactions as well as changing the stoichiometry of reactants. Thermal behavior of the system was also studied.

Porous Aluminas: The biotemplate method for the synthesis of stable high surface area aluminas

Development of porous alumina has been the objective of numerous studies in recent decades, due to the intrinsic properties of aluminium oxide, such as high melting point, low thermal conductivity, chemical inertness and corrosion resistance which, in addition to a high surface area and permeability, make aluminas being used for many different industrial and technical applications. The crystallographic and textural stability of alumina acquires significant importance in those processes involving high temperatures; however, most of the synthesis methods yield metastable oxides of little interest in high-temperature processes due to the transformation to alpha phase, with the consequent reduction in surface area. The present article reviews diverse procedures for obtaining porous alumina with high specific surface area, including methods and strategies for preparing high surface alpha-alumina. Within this framework, the paper analyzes the results obtained through bioreplica of lignocellulosic materials. This technology allows preparing aluminas with the complex structural hierarchy of the lignocellulosic templates.

The aim of this study is to elucidate the coarsening kinetics involved during densification of fine-grained pure α-alumina by spark plasma sintering. Low temperature and short dwell time sintering conditions were used to preserve the nanocrystalline structure of the starting commercial powder (about 50 nm). Notwithstanding the above, submicron grain coarsened microstructures have been developed. The microstructure evolution of alumina under different sintering conditions points to a nanograin rotation densification mechanism as being responsible for the fast grain growth observed.

The aim of this review article on recent developments of mechanochemistry (nowadays established as a part of chemistry) is to provide a comprehensive overview of advances achieved in the field of atomistic processes, phase transformations, simple and multicomponent nanosystems and peculiarities of mechanochemical reactions. Industrial aspects with successful penetration into fields like materials engineering, heterogeneous catalysis and extractive metallurgy are also reviewed. The hallmarks of mechanochemistry include influencing reactivity of solids by the presence of solid-state defects, interphases and relaxation phenomena, enabling processes to take place under non-equilibrium conditions, creating a well-crystallized core of nanoparticles with disordered near-surface shell regions and performing simple dry time-convenient one-step syntheses. Underlying these hallmarks are technological consequences like preparing new nanomaterials with the desired properties or producing these materials in a reproducible way with high yield and under simple and easy operating conditions. The last but not least hallmark is enabling work under environmentally friendly and essentially waste-free conditions (822 references).

The thermal degradation kinetics of several ethylene–propylene copolymers (EPM) and ethylene–propylene–diene terpolymers (EPDM), with different chemical compositions, have been studied by means of the combined kinetic analysis. Until now, attempts to establish the kinetic model for the process have been unsuccessful and previous reports suggest that a model other than a conventional nth order might be responsible. Here, a random scission kinetic model, based on the breakage and evaporation of cleavaged fragments, is found to describe the degradation of all compositions studied. The suitability of the kinetic parameters resulting from the analysis has been asserted by successfully reconstructing the experimental curves. Additionally, it has been shown that the activation energy for the pyrolysis of the EPM copolymers decreases by increasing the propylene content. An explanation for this behavior is given. A low dependence of the EPDM chemical composition on the activation energy for the pyrolysis has been reported, although the thermal stability is influenced by the composition of the diene used.

The Ozawa’s generalized time concept and YZ-master plots as a convenient tool for kinetic analysis of complex processes

The concept of generalized time θ=∫exp(−Ea/RT)dt θ = ∫ exp ( − E a / RT ) d t in non-isothermal kinetics was introduced by Ozawa in 1965, together with the well-known isoconversional plot, i.e., Ozawa plot. The generalized time is the key concept to tie the kinetic data under varying temperature to the kinetic relationship at a constant temperature. It is well known that many processes studied by thermal analysis and calorimetry reveal a complex nature. Therefore, the generalized time concept seems to be very useful for the description of the change in the rate behavior depending on the fractional conversion. Using the concept of θ, three kinds of experimental master plots can be formalized in differential, integral, and multiplied forms. Among others, combination of the differential and multiplied master plots, y(α) = (dα/dθ) and z(α) = (dα/dθ)θ, show a high performance to discriminate the kinetic model based on the maxima condition of y(α y*) and z(α z*). The α y* − α y* kinetic plot is a useful tool to visualize the complexity of the kinetic process and to determine the most suitable kinetic model. The usefulness of α y* − α y* kinetic plot and the YZ-master plots is illustrated as exemplified by the kinetic analyses of complex crystallization processes of the as-prepared, thermally and mechanically treated amorphous zirconia.

Kinetic studies in solid state reactions by sample-controlled methods and advanced analysis procedures

A comparative study of both conventional rising temperature and sample-controlled methods, like constant rate thermal analysis (CRTA), is carried out after analyzing a set of solid state reactions using both methods. It is shown that CRTA avoids the influence of heat and mass transfer phenomena for a wide range of sample sizes leading to reliable kinetic parameters. On the other hand, conventional rising temperature methods yield α–T plots dependent on experimental conditions, even when using samples sizes smaller than 2 mg. Moreover, it is shown that the discrimination of overlapping processes is dramatically improved using sample-controlled methods instead of conventional heating procedures. An advanced method for performing the kinetic analysis of complex processes from a single CRTA experiment is proposed.

The literature data on the superplastic deformation of high purity yttria stabilised tetragonal zirconia polycrystals is reviewed in detail. It is shown that, based on the existence of a threshold stress, the single mechanism of grain boundary sliding (GBS) accommodated by diffusional processes can explain the superplasticity of these materials over all the ranges of temperature, stress, grain size, and surrounding atmosphere that have been studied. The origin of the threshold stress and its quantitative dependence on temperature and grain size is explained in terms of the segregation of yttrium atoms at the grain boundaries. A new model for GBS accommodated by lattice or grain-boundary diffusion is presented which can explain the transition of the stress exponent from 2 to 1.

Experimental results are reported on the (Ca-looping) multicyclic CO2 capture of CaO and nanosilica/CaO composites derived from Ca(OH)2 and nanosilica/Ca(OH)2 dry mixtures subjected in situ to linear and constant rate thermal analysis (CRTA) preheating programs in either air or air/CO2 atmospheres. By means of CRTA preheating the rates of the reactions taking place during pretreatment are kept at a constant and small value along the entire process. In agreement with a pore skeleton model, previously proposed in the literature for explaining the behavior of natural limestones thermally pretreated, our results suggest that air/CO2-CRTA pretreatment yields a thermally stable hard skeleton of poorly reactive CaO on which a soft skeleton of reactive CaO would be supported. The sorbent subjected to this preheating program exhibits a reactivation in the very first carbonation/calcination cycles, after which CaO conversion decays slowly with the cycle number. In contrast, linearly or air-CRTA preheated sorbents show a significant decrease of CaO conversion within the first cycles. In the latter case, CaO multicyclic conversion fits well to a model where it is assumed that the progressive reduction of surface area as the number of carbonation/calcination cycles is increased obeys to sintering of the preheated sorbent skeleton as it is subjected to repeated calcinations during cycling. In the former case, CaO conversion data conforms to the prediction by a model in which the loss of surface area is mainly due to sintering of a nascent CaO soft skeleton regenerated in the diffusive carbonation phase, which is enhanced by the air/CO2-CRTA pretreatment. As regards the effect of nanosilica, the results indicate that it slows down CaO sintering during pretreatment, which hinders the development of a stable CaO skeleton thus hampering reactivation and stabilization of conversion. On the other hand, as CaO sintering is also lessened during looping calcination, nanosilica is useful to increase the absolute values of CaO conversion.

Nanometric powdered TixTa1−xC0.5N0.5-based cermets were fabricated using a mechanically induced self-sustaining reaction and consolidated by spark plasma sintering. Highly dense cermets were obtained, and their chemistry, microstructure and mechanical properties were characterised by X-ray diffraction, scanning electron microscopy, image analysis, microindentation and nanoindentation. The microhardness was found to depend directly on the contiguity and size of the ceramic hard particles. The samples synthesised at the lowest temperature (1150 °C) exhibited more homogeneous microstructures and smaller ceramic particles and the best combination of microhardness and fracture toughness.

The crystallisation and polymorphic properties of three sunflower hard stearins (SHSs) and cocoa butter equivalents (CBEs) formulated by blending SHSs and palm mid fraction (PMF) were studied and compared with those from cocoa butter (CB), to explore their possibilities as confectionery fats. The isothermal crystallisation kinetics of these fats were examined by pNMR and DSC at three different temperatures. All samples studied displayed a two-step crystallisation profile that could be fitted to an exponential-Gompertz equation. Stop-and-return DSC studies showed that SHSs and CBEs exhibited different crystallisation mechanisms according to their triacylglycerol composition, with a quick formation of metastable crystals, followed by a polymorphic transition to the more stable β or β′ forms. X-ray diffraction (XRD) was used to investigate the polymorphic forms of tempered SHSs and CBEs in the long term. In all cases the resulting fats displayed short spacing patterns associated with β polymorphism. These formulations based on SHSs and PMF met all the requirements to be considered as CBEs; therefore they could be used as an alternative to traditional confectionery fats.

A computerized database was created, based on a Geographic Information System (GIS), with hyperlinks to the website for a Rural Development Association (Almería province, Andalusia, Spain). Thus, a catalogue of traditional rural buildings in this particular area was compiled, identifying and characterizing each one, establishing criteria for a dynamic and rational selection. The purpose to select this example was to facilitate their management by public organizations or private individuals, for their reuse, restoration or both. The cataloguing and promotion of rural architecture will contribute to creating jobs by stimulating new economic activity, such as the promotion of cultural tourism, while preserving a valuable source of information on rural culture, recovering local construction techniques, encouraging a sense of community, and making villages and rural areas more attractive to visitors. The assessment of the rehabilitation potential of rural buildings in this region has helped to establish a priority order for their reuse, and so an intervention map has been devised in terms of a “Decision Index” corresponding to each considered building.

Enhanced general analytical equation for the kinetics of the thermal degradation of poly(lactic acid) driven by random scission

An enhanced general analytical equation has been developed in order to evaluate the kinetic parameters of the thermal degradation of poly(lactic acid) (PLA) at various linear heating rates and at constant rate conditions. This improvement consisted of replacing the n-order conversion function by a modified form of the Sestak-Berggren equation f(α) = c(1−α)nαm, which led to better adjustment of experimental data, and also adequately represented the conventional mechanisms for solid-state processes. The kinetic parameters so obtained have been compared to those determined by conventional differential and isoconversional methods. Given that the thermal degradation of PLA has been argued to be caused by random chain scission reactions of ester groups, the conversion function (α) = 2(α1/2−α), corresponding to a random scission mechanism, has been tested.

CO2 multicyclic capture of pretreated/doped CaO in the Ca-looping process. Theory and experiments

We study in this paper the conversion of CaO-based CO2 sorbents when subjected to repeated carbonation–calcination cycles with a focus on thermally pretreated/doped sorbents. Analytical equations are derived to describe the evolution of conversion with the cycle number from a unifying model based on the balance between surface area loss due to sintering in the looping-calcination stage and surface area regeneration as a consequence of solid-state diffusion during the looping-carbonation stage. Multicyclic CaO conversion is governed by the evolution of surface area loss/regeneration that strongly depends on the initial state of the pore skeleton. In the case of thermally pretreated sorbents, the initial pore skeleton is highly sintered and regeneration is relevant, whereas for nonpretreated sorbents the initial pore skeleton is soft and regeneration is negligible. Experimental results are obtained for sorbents subjected to a preheating controlled rate thermal analysis (CRTA) program. By applying this preheating program in a CO2 enriched atmosphere, CaO can be subjected to a rapid carbonation followed by a slow rate controlled decarbonation, which yields a highly sintered skeleton displaying a small conversion in the first cycle and self-reactivation in the next ones. Conversely, carbonation of the sorbent at a slow controlled rate enhances CO2 solid-state diffusion, which gives rise, after a quick decarbonation, to a highly porous skeleton. In this case, CaO conversion in the first cycle is very large but it decays abruptly in subsequent cycles. Data for CaO conversion retrieved from the literature and from further experimental measurements performed in our work are analyzed as influenced by a variety of experimental variables such as preheating temperature program, preheating exposition time, atmosphere composition, presence of additives, and carbonation–calcination conditions. Conversion data are well fitted by the proposed model equations, which are of help for a quantitative interpretation of the effect of experimental conditions on the multicyclic sorbent performance as a function of sintering/regeneration parameters inferred from the fittings and allow foreseeing the critical conditions to promote reactivation. The peculiar behavior of some pretreated sorbents, showing a maximum conversion in a small number of cycles, is explained in light of the model.

Role of Looping-Calcination Conditions on Self-Reactivation of Thermally Pretreated CO2 Sorbents Based on CaO

The conversion of thermally pretreated CaO along successive carbonation/calcination cycles has been investigated, as affected by looping-calcination conditions, by means of Thermogravimetric Analysis (TGA). Sorbent samples have been subjected in situ to a thermal preheating program based on Constant Rate Thermal Analysis (CRTA) by virtue of which decarbonation is carried out at a low controlled rate, which is able to promote self-reactivation in the first carbonation/calcination cycles. Our observations support a pore-skeleton model according to which solid-state diffusion in the first carbonation stages, which is enhanced by thermal pretreatment, gives rise to a soft skeleton with increased surface area. Yet, the results show that self-reactivation is hindered as looping-calcination conditions are harshened. Increasing the looping-calcination temperature and/or the looping calcination time period favors sintering of the soft skeleton and eventually self-reactivation is precluded. A model is developed that retrieves the main features of multicyclic conversion of thermally pretreated sorbents in the first cycles based on the balance between surface area gain due to promoted solid-state diffusion carbonation and surface area loss due to sintering of the soft skeleton in the looping-calcination stage, which can be useful to investigate the critical looping-calcination conditions that nullify self-reactivation. The proposed model allows envisaging the behavior of the sorbent performance as a function of the pretreatment conditions.

In this work, a mechanochemical procedure is proposed as a simple and fast method to synthesize the pure BiFeO3 perovskite phase as a nanostructured material without the need for purification treatments, while the mechanochemical reaction mechanism has been investigated and correlated with that of the conventional solid-state reaction. Thus, different milling conditions have been used as a tool for tailoring the crystallite size of the resulting BiFeO3 nanoparticles. The materials prepared by the mechanochemical reaction could be annealed or sintered without the formation of undesirable phases. Both the ferroelectric and ferromagnetic transitions were observed by DSC. Finally, the dielectric constants of the prepared material at different frequencies as a function of the temperature have been measured, showing that the material is clearly an isolator below 200 °C, characteristic of a high quality BiFeO3 material.

Liquid-phase sintering of Ti(C,N)-based cermets. The effects of binder nature and content on the solubility and wettability of hard ceramic phases

Different commercial TiC–TiN/Co/Ni mixtures were used as raw materials for Ti(C,N) cermets, and the effects of the sintering parameters (binder content, binder nature, sintering time and additives) on the final hard ceramic phase were studied at the sintering temperature of 1400 °C. When Co is used as the binder medium, it is possible to completely convert the starting commercial TiC–TiN mixture into TiCxN1−x. When Ni is used, which exhibits lower solubilising capacity than Co, the total conversion can never be reached and the metallurgical reactions between TiC and TiN during the liquid-phase sintering are more dependent on the sintering time than on the binder content. However, the use of Co–Ni mixtures, showing a synergic effect between the wettability capacity of Ni and the solubilising capacity of Co, enhances the metallurgical reactions at short sintering times.

In this paper, some clarifications regarding the use of model-fitting methods of kinetic analysis are provided in response to the lack of plot linearity and dispersion in the activation energy values for the thermal degradation of polystyrene found in the literature and some results proposing an nth order model as the most suitable one. In the present work, two model-fitting methods based on the differential and integral forms of the general kinetic equation are evaluated using both simulated and experimental data, showing that the differential method is recommended due to its higher discrimination power. Moreover, the intrinsic limitations of model-fitting methods are highlighted: the use of a limited set of kinetic models to fit experimental data and the ideal nature of such models. Finally, it is concluded that a chain scission model is more appropriate than first order.

Effect of sintering time on the microstructure and mechanical properties of (Ti,Ta)(C,N)-based cermets

Complete solid-solution cermets based on titanium–tantalum carbonitride using a starting nominal composition with 80 wt.% of (Ti0.8Ta0.2)(C0.5N0.5) and 20 wt.% of Co were performed by pressure-less sintering at 1550 °C for different times (from 0 to 180 min) in an inert atmosphere. Chemical and phase analyses were conducted using X-ray diffraction (XRD), elemental analysis and energy dispersive X-ray spectrometry (EDX). The binder mean free path and the contiguity of the carbonitride particles were used to rationalise the microstructural effects of the mechanical behaviour. Mechanical characterisation included determining the Vickers hardness, the fracture toughness (conventional indentation microfractures, IM), the dynamic Young's modulus (ultrasonic technique), the biaxial strength (ball on three ball) and a detailed fractographic examination. Finally, the experimental findings were combined with a theoretical fracture mechanics analysis to estimate the critical processing flaw sizes. Binder-less carbonitride clusters, pores and coarse carbonitride grains were the main defects observed and were responsible for the fractures.

Electrical Properties of Stoichiometric BiFeO3 Prepared by Mechanosynthesis with Either Conventional or Spark Plasma Sintering

Phase-pure powders of stoichiometric BiFeO3 have been prepared by mechanosynthesis. Ceramics sintered by either conventional heating in air or spark plasma sintering (SPS) followed by oxidative anneal in air are highly insulating at room temperature with resistivity, extrapolated from the Arrhenius plots, of ~1016 Ωcm and activation energy 1.15(2) eV, comparable with those of a good-quality BiFeO3 single crystal. By contrast, the as-prepared SPS sample without the postsinter anneal shows lower resistivity, e.g., ~1010 Ωcm at 25°C and activation energy 0.67(3) eV, indicating some reduction in the sample by the SPS process. The reason for the high conductivity reported for some ceramic samples in the literature remains unclear at present.

Characterization and repair measures of the medieval building materials of a Hispanic–Islamic construction

This paper focuses on the physical–chemical and mechanical characterization of the building materials of a precious damaged structure, the Salares tower, a Hispanic–Islamic medieval construction located in the South of Spain, an active seismic area. An exhaustive description of the materials has been obtained, enriching the knowledge on historical construction materials. Sophisticated laboratory tests (XRD, SEM, EDX, FTIR, Micro-Raman spectroscopy, DTA and TG) have provided crucial complementary data to use together with traditional laboratory procedures, especially when the damage processes are the main concern. The experimental investigation has allowed a better understanding of the remote origin and of the failure mechanisms of this damaged structure. On the basis of these results, the most adequate repair materials are selected.

Segregation to the grain boundaries in YSZ bicrystals: A Molecular Dynamics study

A Molecular Dynamics study about the segregation of yttrium at 1500 K to a Σ5 grain boundary in 8 mol% YSZ has been performed. Segregation has been induced by explicitly taking into account the excess energy associated to the elastic misfit effect for yttrium cations located nearby the grain boundary planes. After an initial transient, a steady regime is reached, in which the number of yttrium cations does not increase with time. Accumulation of yttrium cations is accompanied by that of zirconium ones and oxygen vacancies at some distance of the grain boundary planes. The changes in the radial distribution functions for different ionic pairs are discussed, as also the effect of segregation on oxygen diffusion along the grain boundaries and in volume. Finally, the possibility that segregated yttrium located at available free sites at the grain boundaries is pointed out.

Cystine-capped CdSe@ZnS nanocomposites: mechanochemical synthesis, properties, and the role of capping agent

Cystine-capped CdSe@ZnS nanocomposites were synthesized mechanochemically with the aim to prepare a material which could be used in medicine for biosensing applications. Although synthesized CdSe@ZnS nanocomposites were capped with l-cysteine, cystine was formed from l-cysteine during the milling process. It was proven that water plays the key role in this oxidative transformation. The novel material was characterized by the complex of physico-chemical methods (FTIR, XPS, SEM, EDX, surface area measurements) and CHNS analysis. The leakage of Cd2+ and Zn2+ ions into physiological solution was also studied.

Comments on “Thermal decomposition of pyridoxine: an evolved gas analysis-ion attachment mass spectrometry study”. About the application of model-fitting methods of kinetic analysis to single non-isothermal curves

Practical usefulness of the kinetic deconvolution for partially overlapped thermal decomposition processes of solids was examined by applying to the co-precipitated basic zinc carbonate and zinc carbonate. Comparing with the experimental deconvolutions by thermoanalytical techniques and mathematical deconvolutions using different statistical fitting functions, performance of the kinetic deconvolution based on an accumulative kinetic equation for the independent processes overlapped partially was evaluated in views of the peak deconvolution and kinetic evaluation. Two-independent kinetic processes of thermal decompositions of basic zinc carbonate and zinc carbonate were successfully deconvoluted by means of the thermoanalytical measurements in flowing CO2 and by applying sample controlled thermal analysis (SCTA). The deconvolutions by the mathematical curve fittings using different fitting functions and subsequent formal kinetic analysis provide acceptable values of the mass-loss fractions and apparent activation energies of the respective reaction processes, but the estimated kinetic model function changes depending on the fitting functions employed for the peak deconvolution. The mass-loss fractions and apparent kinetic parameters of the respective reaction processes can be optimized simultaneously by the kinetic deconvolution based on the kinetic equation through nonlinear least square analysis, where all the parameters indicated acceptable correspondences to those estimated through the experimental and mathematical deconvolutions. As long as the reaction processes overlapped are independent kinetically, the simple and rapid procedure of kinetic deconvolution is useful as a tool for characterizing the partially overlapped kinetic processes of the thermal decomposition of solids.

Allochthonous red pigments used in burial practices at the Copper Age site of Valencina de la Concepción (Sevilla, Spain): characterisation and social dimension

The use of red pigments linked to burial practices is widely documented in the Iberian prehistoric record and very often it has been traditionally interpreted as a ritual practice entailing the utilisation of local raw materials (iron oxides). Some research works, nevertheless, have also detected the use of red pigments which can only be interpreted as allochthonous. The red pigments spread over a single inhumation in a monumental Megalithic tomb surrounding Valencina de la Concepción Copper Age settlement was studied by means of X-ray diffraction, field emission scanning electron microscopy with energy dispersive X-ray spectroscopy, X-ray microfluorescence, micro-Raman and Fourier transform infrared spectroscopies. This approach allowed characterising the red pigments as cinnabar, mixed with tiny amounts of iron oxides. The presence of cinnabar, a product that was necessarily imported, in a context of an exceptional set of grave goods, suggests that the use of cinnabar was linked not only to ritual but also to practices related to the display of social status.

Clarifications regarding the use of model-fitting methods of kinetic analysis for determining the activation energy from a single non-isothermal curve

This paper provides some clarifications regarding the use of model-fitting methods of kinetic analysis for estimating the activation energy of a process, in response to some results recently published in Chemistry Central journal.
Findings

The model fitting methods of Arrhenius and Savata are used to determine the activation energy of a single simulated curve. It is shown that most kinetic models correctly fit the data, each providing a different value for the activation energy. Therefore it is not really possible to determine the correct activation energy from a single non-isothermal curve. On the other hand, when a set of curves are recorded under different heating schedules are used, the correct kinetic parameters can be clearly discerned.
Conclusions

Here, it is shown that the activation energy and the kinetic model cannot be unambiguously determined from a single experimental curve recorded under non isothermal conditions. Thus, the use of a set of curves recorded under different heating schedules is mandatory if model-fitting methods are employed.

Mechanochemical synthesis of Sb2S3 and Bi2S3 nanoparticles

The mechanochemical synthesis of Sb2S3 and Bi2S3 nanoparticles has been studied, starting from the corresponding metals and sulfur and using high-energy mechanochemical processing in a planetary laboratory mill. XRD, specific surface area measurement, SEM and TEM (HRTEM) with ED were used for the characterization of the nanoparticles. The XRD patterns confirmed the production of Sb2S3 (JCPDS 42–1393, orthorhombic) and Bi2S3 (JCPDS 17–320, orthorhombic) nanopowders. The transformation is about three times faster in the Bi–S than in the Sb–S system. The kinetics of the reaction has been determined from XRD line intensities. The grain size is about 30 nm for Sb2S3 and 24 nm for Bi2S3. The particles are highly agglomerated due to their nanometer size consequent large specific surface area. Unlike more conventional methods, mechanochemical synthesis is a simple and fast alternative for the preparation of these nanopowders that can be carried out at ambient temperature and atmospheric pressure.

Influence of the milling parameters on the mechanical work intensity in planetary mills

The formation of ZnSe via a mechanically-induced self-sustaining reaction (MSR) from a Zn/Se mixture showed that only size reduction and mixing of the reactants without product formation occurred during the induction period prior to ignition. Therefore, all mechanical energy supplied by the planetary mill during this time, called the ignition time (tig), was used exclusively in the activation of the reactants. This system was chosen to study the dependence of tig on the main parameters characterising the milling intensity of planetary mills. The variation of the ignition time with the process conditions reflected changes in the mechanical dose rate of the planetary mill. A direct relationship between the inverse of the ignition time and the power of the planetary mill was established, which allows the validation of theoretical models proposed in the literature for the energy transfer in milling devices and the comparison of milling equipment efficiencies.

Generalized master plots as a straightforward approach for determining the kinetic model: The case of cellulose pyrolysis

The thermal degradation of cellulose is a complex reaction and, despite the large amount of work by many investigators during the last decades, the actual understanding of the thermal decomposition kinetics is still very limited. Thus, while several mechanisms have been proposed to describe the process, the real model has not yet been clearly identified. In this paper, a set of experimental curves recorded under different heating schedules, i.e., linear heating rate, isothermal and constant rate thermal analysis (CRTA), has been analyzed using isoconversional and master plots methodology to discriminate the kinetic model followed by the reaction.

Colour and ultrasound propagation speed changes by different ageing of freezing/thawing and cooling/heating in granitic materials

In the present work we determined the chromatic coordinates (L*, a*, b*) and ultrasound propagation speeds on the three spatial planes (Vx, Vy, Vz) of three ornamental granites (Aqueduct of Segovia, Spain) before, during, and after being subjected to 70 cycles of two types of accelerated ageing (typical of cold regions): a) freezing/thawing and cooling/heating (T1), and b) freezing/thawing and cooling/heating + salt crystallization (T2). A multivariate technique (Canonical Biplot) was applied to the data obtained, with the observation of significant variations between the two types of accelerated artificial ageing as compared with those obtained in quarry rock in the three chromatic coordinates (L*, a*, b*). With regard to the ultrasound propagation speed, we only detected differences in the results of the T2 artificial ageing treatment with respect to those of quarry rock. This fact is confirmed by the estimated data of resistance to compression.

Quantum-Mechanical Study on the Aquaions and Hydrolyzed Species of Po(IV), Te(IV), and Bi(III) in Water

A systematic study of [M(H2O)n(OH)m]q+ complexes of Te(IV) and Bi(III) in solution has been undertaken by means of quantum mechanical calculations. The results have been compared with previous information obtained for the same type of Po(IV) complexes ( J. Phys. Chem. B 2009, 113, 487) to get insight into the similarities and differences among them from a theoretical view. The evolution of the coordination number (n + m) with the degree of hydrolysis (m) for the stable species shows a systematic decrease regardless the ion. A general behavior on the M–O distances when passing from the gas phase to solution, represented by the polarizable continuum model (PCM), is also observed: RM–O values corresponding to water molecules decrease, while those of the hydroxyl groups slightly increase. The hydration numbers of aquaions are between 8 and 9 for the three cations, whereas hydrolyzed species behave differently for Te(IV) and Po(IV) than for Bi(III), which shows a stronger trend to dehydrate with the hydrolysis. On the basis of the semicontinuum solvation model, the hydration Gibbs energies are −800 (exptl −834 kcal/mol), −1580 and −1490 kcal/mol for Bi(III), Te(IV), and Po(IV), respectively. Wave function analysis of M–O and O–H bonds along the complexes has been carried out by means of quantum theory of atoms in molecule (QTAIM). Values of electron density and its Laplacian at bond critical points show different behaviors among the cations in aquaions. An interesting conclusion of the QTAIM analysis is that the prospection of the water O–H bond is more sensitive than the M–O bond to the ion interaction. A global comparison of cation properties in solution supplies a picture where the Po(IV) behavior is between those of Te(IV) and Bi(III), but closer to the first one.

Microcalorimetric study of the annealing hardening mechanism of a Cu–2.8Ni–1.4Si (at%) alloy

The precipitation processes in a Cu–2.8 at% Ni–1.4 at% Si alloy were studied using differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and microhardeness measurements. The analysis of the calorimetric curves from room temperature to 900 K shows the presence of one exothermic reaction attributed to the formation of δ-Ni2Si particles in the copper matrix that was confirmed by Transmission Electron Microscopy (TEM) and EDS microanalysis. The activation energies calculated for the precipitation of δ-Ni2Si was lower than the ones corresponding to diffusion of nickel and silicon in copper. A correlation between of microhardness of the alloy and the formation of δ-Ni2Si particles has been found.

Mechanochemical synthesis of bismuth selenides (BiSe, Bi 2Se 3) was performed by high-energy milling of bismuth and selenium powders in a planetary ball mill. The particle size distribution and the specific surface area of Bi/Se and 2Bi/3Se powder mixtures were analysed at increasing milling time. The products were characterized by X-ray diffraction, differential scanning calorimetry and transmission electron microscopy. The presence of bismuth selenide phases was observed after only 1 min of milling and full conversion into hexagonal BiSe phase (nevskite) and rhombohedral Bi 2Se 3 phase (paraguanajuatite) was reached after 10 min of milling. The nanocrystalline nature of both mechanochemically synthesised bismuth selenides was confirmed and their optical band gap energies were obtained on the basis of the recorded absorption spectra in UV-Vis spectral region.

Obituary: Prof. Andrés Ortega

Prof. Andrés Ortega passed away on last January after a painful and long illness. He was Professor of Inorganic Chemistry at the University of Seville (Spain) and was an outstanding researcher in the field of solid state reaction kinetics, an area to which he devoted his entire career since 1983, when he submitted his PhD thesis entitled ‘Critical study of non-isothermal methods for the kinetic analysis of solid-state reactions’. During his post doc stage and collaboration with Prof. Jean Rouquerol, his interest was raised by the Sample Controlled Thermal Analysis (SCTA) technique and its application to the kinetic study of solid state reactions, this latter one developed in Seville along with Prof. José Manuel Criado. A paper from this period should be highlighted: ‘Correlation between the shape of controlled-rate thermal analysis curves and the kinetics of solid-state reactions’ [Thermochimica Acta 157 (1990) 171], the most cited one in his research career. Most of his scientific production was published in Thermochimica Acta and in the Journal of Thermal Analysis and Calorimetry. A tireless professional, he remained active until a few weeks before dying. Being seriously ill he developed a method for the kinetic analysis of reactions with variable activation energies that notably simplifies the previous one proposed by Vyazovkin. The results were published in Thermochimica Acta under the title ‘A simple and precise linear integral method for isoconversional data’ [Thermochim. Acta 474 (2008) 81]. The high number of citations of this article – according to the ISI WEB of Knowledge – in spite of the short time elapsed since it was published reveals its impact within the scientific community.

He was also very much involved in teaching duties, developing new subjects and applying new teaching methodologies. He chaired two important academic positions at the University of Seville related to his works on teaching and educational sciences, as Director of the Institute of Educational Science and as Chairman of the Committee on Education of the University.

Though he sometimes appeared to be reserved, Andrés was a kind man, always ready to help in any problem that was presented to him. With a critical attitude and many cultural interests, he had a vast knowledge and a great ability to interpret the most diverse questions, frequently presenting a reasoning alternative to those commonly established. This was a continuous source of enrichment for both his friends and colleagues, who never will forget him.

Silver nanoparticles are emerging as a powerful tool in bioimaging applications owing to their unique plasmonic properties i.e., extremely high molar extinction coefficients, resonant Rayleigh scattering and enhanced local electromagnetic fields. Through the optimization of these properties, by controlling composition, size, shape, and interparticle spacing of nanoparticles and their assemblies, highly enhanced local electromagnetic fields in the vicinity of nanoparticles are achievable giving rise to IR, Raman and fluorescence surface enhanced spectroscopies (SEIRS, SERS and MEF, respectively).

There is a growing interest in nanoparticles as carriers of chemotherapeutic agents in order to improve their administration and minimize their side effects. Despite the fact that silver nanoparticles can be conjugated to therapeutic agents, offering additionally advantages due their unique and tunable optical properties, few examples have been described yet.

Synthesis of a TiCN–SiC polyhedron and elongated crystals nanopowder at low nitrogen concentration

At room temperature diluted TiCl4 and CCl4 were reduced by sodium particles and mixed with a polycarbomethylsilane (PCS) solution to yield a precursor. It was dried and subsequently annealed at 1300 °C, 1400 °C and 1450 °C in a tube furnace using argon with 10 ppm N2. After the 1450 °C annealing a nanocrystalline powder of TiC0.5N0.5–SiC polyhedron and elongated crystals was obtained. At the low nitrogen concentration during annealing a gradual nitration is proposed. It is promoted by carbon gaseous species, precursor oxidation, a sufficient temperature and a summarised nitrogen surplus compared to the titanium and carbon amount.

This paper reports an improved procedure for synthesis of silicon carbide nanopowders from silica by carbothermic reduction under fast microwave-induced heating. The powders have been prepared by direct solid-state reaction in a 2.45 GHz microwave field in nitrogen atmosphere after 40 h milling. For the first time, the formation of silicon carbide (beta-SiC) as a major phase can be achieved at 1200 degrees C in 5 min of microwave exposure, resulting in nano sized particles ranging from 10 to 40 nm under optimized synthesis condition. The Rietveld quantitative phase-composition analysis confirmed that the major SiC polytype is cubic SiC (beta-SiC) with 98.5(4) weight fraction and the remained is minor hexagonal SiC polytypic (alpha-SiC) phases. Therefore this method is the most efficient one for SiC powder synthesis in terms of energy and time saving as well as preparation of SiC nano powders.

In Situ Synthesis of Ceramic Composite Materials in the Ti-B-C-N System by a Mechanically Induced Self-Sustaining Reaction

The synthesis of multicomponent ceramic materials in the titanium-diboride-carbide-nitride-carbonitride system by the mechanochemical process known as the mechanically induced self-sustaining reaction (MSR) was investigated. Ceramic composite powders containing TiB 2and TiC, TiN or TiC xN 1-xwere prepared from a blended mixture of the elements by exploiting the highly exothermic nature of the formation reactions. The synthesis of the composite materials was made possible by the ability of the MSR to simultaneously induce independent self-sustaining reactions, generating a mixture of ceramic phases. The composition of the ceramic composites was designed using the initial atomic ratio of the reactants, and the achieved microstructure was characterized by TiB 2particles in the micrometric range, surrounded by submicrometric and nanometric TiC, TiN, or TiC xN 1-xcrystals.

Absence of the core-rim microstructure in TixTa1-xCyN1-y-based cermets developed from a pre-sintered carbonitride master alloy

(Ti,Ta)(C,N) solid solution-based cermets with cobalt as the binder phase were synthesised by a two-step milling process. The titanium-tantalum carbonitride solid solution (the ceramic phase) was obtained via a mechanically induced self-sustaining reaction (MSR) process from stoichiometric elemental Ti, Ta, and graphite powder blends in a nitrogen atmosphere. Elemental Co (the binder phase) was added to the ceramic phase, and the mixture was homogenised by mechanical milling (MM). The powdered cermet was then sintered in a tubular furnace at temperatures ranging from 1400°C to 1600°C in an inert atmosphere. The chemical composition and microstructure of the sintered cermets were characterised as ceramic particles grown via a coalescence process and embedded in a complex (Ti,Ta)-Co intermetallic matrix. The absence of the typical core-rim microstructure was confirmed.

CdSe@ZnS nanocrystals have been prepared by a two-step solid state mechanochemical synthesis. CdSe prepared from elements in the first step is mixed with ZnS synthesized from zinc acetate and sodium sulfide in the second step. The crystallite size of the new type CdSe@ZnS nanocrystals determined by X-ray diffraction Rietveld refined method was 35 nra and 10 Jam for CdSe and ZnS, respectively. Energy dispersive/transmission electron microscopy/energy dispersive spectroscopy methods show good crystallinity of the nanoparticles and scanning electron microscopy elemental mapping illustrate consistent distribution of Cd, Se, Zn and S elements in the bulk of samples. UV-VIS spectra show an onset at 320 urn with calculated bandgap 3.85 eV. This absorption arises from the vibration modes of Zn-S bonds. The nanocrystals show the blue shift from the bandgap of bulk ZnS (3.66 eV). The synthesized CdSe@ZnS nanocrystals have been tested for dissolution, cytotoxicity and L-cysteine conjugation. The dissolution of Cd was less than 0.05 mu g mL(-1) (in comparison with 0.8 mu g mL(-1) which was evidenced for CdSe alone). The very low cytotoxic activity for selected cancer cell lines has been evidenced. CdSe@ZnS nanocrystals coated with L-cysteine are water-soluble and have a great potential in biomedical engineering as fluorescent labels.

Single wall carbon nanotube reinforced yttria stabilized zirconia ceramic materials have been obtained by means of spark plasma sintering technique. Single wall carbon nanotubes were treated in an acid solution before mixing with zirconia powders to obtain a uniform distribution of both powders. This method allows obtaining ceramic materials with a grain size between 200 nanometers and 1 micron and with a grain size distribution which depends on processing conditions. This new route opens a new perspective for new ceramic composites tailoring with enhanced mechanical properties as structural materials

Enhancement of Fast CO2 Capture by a Nano-SiO2/CaO Composite at Ca-Looping Conditions

In this paper we show the performance of a new CO 2 sorbent consisting of a dry physical mixture of a Ca-based sorbent and a SiO 2 nanostructured powder. Thermo-gravimetric analysis (TGA) performed at conditions close to the Ca-looping process demonstrate that the rate of CO 2 capture by the mixture is enhanced during the fast carbonation stage of practical interest in applications. Moreover, the residual capture capacity of the mixture is increased. SEM/EDX, physisorption, and XRD analyses indicate that there is a relevant interaction between the nanostructured SiO 2 skeleton and CaO at high temperatures, which serves to improve the efficiency of the transfer of CO 2 to small reactive pores as well as the stability of the sorbent pore structure.

Development of multicomponent-multiphase materials based on (Ti,Ta,Nb)CxN1-x carbonitride solid solutions

A set of powdered cermets based on (Ti,Ta,Nb)C xN 1-x carbonitride solid solutions were synthesized from mixtures of elemental powders by a mechanically induced self-sustaining reaction (MSR) method and subsequently sintered using a pressureless method. Differing nominal compositions of the hard phase were used, and the nature of the metallic-binder phase (Co, Ni, or Co-Ni) was varied. For comparative purposes, the design of the material was performed using two different synthesis pathways. The composition and microstructure of the ceramic and binder phases before and after sintering were analyzed and related to the microhardness of the material, which was found to increase with increasing contiguity of the hard phase and with decreasing particle size.The samples synthesized in one step (SERIES 2) showed higher microhardness and a more homogeneous microstructure with smaller particle size of the hard phase due to the presence of Ti, Ta, and Nb in the molten binder that hindered ceramic growth during liquid phase sintering.

Nanoclay Nucleation Effect in the Thermal Stabilization of a Polymer Nanocomposite: A Kinetic Mechanism Change

The enhanced thermal stability of polymer-clay nanocomposites over the original polymers is one of their most interesting features, and it has been profusely studied within the last decades. Here, a thorough kinetic analysis of polystyrene and a montmorillonite-polystyrene nanocomposite has been performed making use of state-of-the-art kinetic procedures. It has been found that the degradation mechanism changes from a chain scission process for the polymer to a complex two-step nucleation-driven reaction for the nanocomposite. This mechanism change can explain the delayed onset of degradation found in the nanocomposite. Moreover, observation by transmission electron microscopy (TEM) has shown that the clay platelets within the composite could act as nucleation centers for the decomposition.

Nanometer-sized titanium-niobium carbonitride powders (Ti yNb 1-yC xN 1-x) with different Ti/Nb atomic ratios were obtained by a mechanically induced self-sustaining reaction, and sintered by spark plasma sintering technique at 1500°C for 1min in a vacuum atmosphere. Mechanical properties such as hardness and Young's modulus were determined by nanoindentation technique and friction and wear coefficients assessed by ball-on-disk testing using alumina ball in dry sliding conditions. The fracture surface and wear tracks of samples were examined by scanning electron microscopy. Results showed that it is possible to obtain dense monolithic ceramics from the solid solution (Ti yNb 1-yC xN 1-x) with good mechanical properties and excellent wear resistance. The optimum values of nanomechanical properties were found for the Ti 0.3Nb 0.7C 0.5N 0.5 ceramic composition, which exhibited a high hardness over 26.0GPa and Young's modulus around 400GPa.

Monophase nanocrystalline powders belonging to the La1−xSrxMnO3±δ system (0≤x≤1) with a perovskite structure have been obtained by mechanochemistry synthesis using a planetary ball milling equipment from La2O3, SrO, and Mn2O3 mixtures. The solid state reaction was complete after one hour of milling treatment. For all the compositional range, the diffraction domain was very small and the structure appeared as a pseudo cubic perovskite. After annealing at 1100 °C under static air, the symmetry evolution due to the La substitution by Sr was analyzed by X-ray and electron diffraction. Samples with x=0, 0.25, 0.5, and 0.75 were assigned to R-3c space group (1 6 7) in the rhombohedral system and perovskite structure. However, the symmetry of the last term of the system (x=1), SrMnO3±δ sample, changed to P63/mmc space group (1 9 4) in the hexagonal system. The terms with x=0.8, 0.85, and 0.9 presented mainly rhombohedral symmetry.

Nanostructured Spark Plasma Sintered Ce-TZP Ceramics

In this work, spark plasma sintering (SPS) of 10 mol% CeO 2-doped ZrO 2 nanocrystalline powders, obtained by a two-step synthesis procedure, allows the preparation of fully densified nanostructured ceramics. The CeO 2-ZrO 2 powders with particle size below 100 nm are obtained after CeO 2 deposition on hydrothermally synthesized ZrO 2 particles by the impregnation method. Tetragonal CeO 2-ZrO 2 ceramics are obtained when sintering at 1200°C without holding time. A graded material containing tetragonal, monoclinic, and pyrochlore phases are obtained when sintering at 1200°C and for 5 min holding time. This is explained in terms of the gradual reduction of Ce 4+ to Ce 3+ species by carbon in the graphite environment during SPS. With the successful combination of the stabilizer coating technique and SPS, we achieve not only the stabilization of the tetragonal phase in the ceramics, but also good control of the grain size, by producing nanostructured ceramics with 40-70 nm grain sizes.

Inverse core-rim microstructure in (Ti,Ta)(C,N)-based cermets developed by a mechanically induced self-sustaining reaction

Cermets with a nominal composition (Tia(0.8)Ta(0.2)C(0.5)N(0.5)-20 wt.% Co) were synthesised by a mechanically induced self-sustaining reaction (MSR) process from stoichiometric elemental powder blends. The MSR allowed the production of a complex (Ti,Ta)(C,N) solid solution, which was the raw material used for the sintering process. The pressureless sintering process was performed at temperatures between 1400 degrees C and 1600 degrees C in an inert atmosphere. The microstructural characterisation showed a complex microstructure composed of a ceramic phase with an unusual inverse core-rim structure and a Ti-Ta-Co intermetallic phase that acted as the binder.

Thermal behaviour of ground and unground acid leached vermiculite

Acid leaching of vermiculite is an interesting procedure to prepare high surface area porous silica. Thermal behaviour of unground and ground vermiculite leached with HCl solutions has been studied by TG, DTA, ETA and high temperature XRD. Important differences have been observed in the thermal behaviour of unground and ground vermiculite after the acid treatments. Thus, for the acid-treated unground vermiculite, dehydrated vermiculite, enstatite and cristobalite were formed during the heating, while for the acid-treated ground vermiculite only iron oxides and cristobalite phases were observed. Structural modifications due to acid treatment were responsible for changes in the transport properties determined by ETA for the vermiculite samples.

XRF, μ-XRD and μ-spectroscopic techniques for revealing the composition and structure of paint layers on polychrome sculptures after multiple restorations

This paper presents the novel application of recently developed analytical techniques to the study of paint layers on sculptures that have been restored/repainted several times across centuries. Analyses were performed using portable XRF, μ-XRD and μ-Raman instruments. Other techniques, such as optical microscopy, SEM-EDX and μ-FTIR, were also used. Pigments and other materials including vermilion, minium, red lac, ivory black, lead white, barium white, zinc white (zincite), titanium white (rutile and anatase), lithopone, gold and brass were detected. Pigments from both ancient and modern times were found due to the different restorations/repaintings carried out. μ-Raman was very useful to characterise some pigments that were difficult to determine by μ-XRD. In some cases, pigments identification was only possible by combining results from the different analytical techniques used in this work. This work is the first article devoted to the study of sculpture cross-section samples using laboratory-made μ-XRD systems.

In the present manuscript the authors have systematically investigated the composition and microstructure of a series of ternary nitrides (TixV1-xNy) (0.0 <= x <= 1.0) prepared by mechanosynthesis, using XRD, SEM, EELS, XAS and TGA. The ternary titanium-vanadium nitride (TixV1-xNy) has been obtained in all range of compositions by the mechanical treatment of the two metals under nitrogen pressure in a planetary mill with a maximum milling time of 3 h and without any post-heating treatment. The materials' microhardnesses were measured after sinterisation and compared to those reported in the literature for these types of materials. When compared with the previously reported data for bulk samples, these values are similar or higher for compositions within the range x = 0.5 to x = 0.77 (TixV1-xN).

Degradation of Two Historic Buildings in Northern Spain by Formation of Oxalate and Sulphate-Based Compounds

This study focused on the degradation processes for two historic buildings, one in a rural and one in an urban environment. Samples collected from the Romanesque Church of Torme and from two areas of the Cathedral of Burgos were studied by using optical and electron microscopy, x-ray spectrometry, x-ray diffraction, Fourier transform infrared spectroscopy and thermal analysis (TG/DTA/DTG). As result of the action of microorganisms, weddellite and whewellite were found to have formed over the entire external walls of the Church of Torme, built with dolomitic rock. Gypsum, formed by the effects of atmospheric pollution, appeared on lime plasters applied as protective coatings on the external stones of Burgos' Cathedral. Also discussed in this study is the different composition of these plasters, based on the use of calcareous and siliceous aggregates.

Analysis of the restoration of an historical organ: The case study of the Cavaillé-Coll organ of La Merced Church in Burgos, Spain

The restoration of the Cavaille-Coll Romantic organ housed in La Merced Church of Burgos, Spain is described in this paper. The organ was affected by a fire that took place in the church. The effect of the fire on the pipes differed depending on their location within the instrument. A combination of analytical techniques (X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray analysis, particle-induced X-ray emission, metallography, and specific density) allowed the accurate determination of the microstructures and compositions of the alloys used to make the different pipes of the organ, some of which had a high tin content and others which had a high lead content. The most damaged pipes were replaced by reconstructed pipes made out of metallic sheets of the same composition as the originals, to ensure a historically accurate sound.

Non-isothermal microcalorimetric evaluations in quenched and in cold-rolled Cu-9Ni-5.5Sn alloys

The thermal aging of both a quenched and a cold rolled homogeneous supersaturated Cu-9 % wt Ni-5.5 wt % Sn alloy has been studied from differential scanning calorimetry (DSC) and microhardness measurements. An increase of the hardness during the aging of the quenched sample, because of the precipitation of a γ' phase, takes place. On the contrary, no hardness increase was observed during the aging of the cold rolled sample. A theoretical analysis of the enthalpy determined from the first DSC exothermic peak suggests that a segregation of the solute towards the dislocations occurs during the aging of the cold rolled alloy. The values of the n Avrami-Erofeev coefficients estimated from the kinetic analysis supports the above interpretations.

An improved model for the kinetic description of the thermal degradation of cellulose

In spite of the large amount of work performed by many investigators during last decade, the actual understanding of the kinetics of thermal degradation of cellulose is still largely unexplained. In this paper, recent findings suggesting a nucleation and growth of nuclei mechanism as the main step of cellulose degradation have been reassessed and a more appropriate model involving chain scission and volatilization of fragments has been proposed instead. The kinetics of cellulose pyrolysis have been revisited by making use of a novel kinetic method that, without any previous assumptions regarding the kinetic model, allows performing the kinetic analysis of a set of experimental curves recorded under different heating schedules. The kinetic parameters and kinetic model obtained allows for the reconstruction of the whole set of experimental TG curves.

This work shows the benefits of characterizing historic paintings via compositional and microtextural data from micro-X-ray diffraction (μ-XRD) combined with molecular information acquired with Raman microscopy (RM) along depth profiles in paint stratigraphies. The novel approach was applied to identify inorganic and organic components from paintings placed at the 14th century Islamic University—Madrasah Yusufiyya—in Granada (Spain), the only Islamic University still standing from the time of Al-Andalus (Islamic Spain). The use of μ-XRD to obtain quantitative microtextural information of crystalline phases provided by two-dimensional diffraction patterns to recognize pigments nature and manufacture, and decay processes in complex paint cross sections, has not been reported yet. A simple Nasrid (14th century) palette made of gypsum, vermilion, and azurite mixed with glue was identified in polychromed stuccos. Here also a Christian intervention was found via the use of smalt, barite, hematite, Brunswick green and gold; oil was the binding media employed. On mural paintings and wood ceilings, more complex palettes dated to the 19th century were found, made of gypsum, anhydrite, barite, dolomite, calcite, lead white, hematite, minium, synthetic ultramarine blue, and black carbon. The identified binders were glue, egg yolk, and oil.

Influence of Al2O3 reinforcement on precipitation kinetic of Cu–Cr nanocomposite

In this paper, the kinetic of precipitation process in mechanically alloyed Cu-1 wt.% Cr and Cu-1 wt.% Cr/3 wt.% Al2O3 solid solution was compared using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The ageing kinetics in Cu–Cr and Cu–Cr/Al2O3 can be described using Johnson–Mehl–Avrami (JMA) and Sestak–Berggren (SB) models, respectively. These different behaviors have been discussed in details. It was found that in presence of Al2O3 reinforcement, the ageing activation energy is decreased and the overall ageing process is accelerated. This behavior is probably due to higher dislocation density previously obtained during ball milling and Al2O3–Cu interface. TEM observations confirm that Al2O3–Cu interface and structural defects act as a primary and secondary nucleation sites, respectively.

The complete range of Ti5Si3–Ti5Ge3 solid solutions was synthesised from elemental mixtures of Ti, Si, and Ge under an inert atmosphere via mechanically induced self-sustaining reactions (MSR). The stoichiometry of Ti5Si3−xGex solid solutions was controlled by adjusting the Si/Ge ratio of the initial mixture. The chemical composition and lattice parameters of the materials confirmed that Ti5Si3–Ti5Ge3 solid solutions with good chemical homogeneity could be produced via MSR.

Old and modern pigments identification from a 14th century sculpture by Micro-Raman

The chromatic characterization of the external part of the sculpture showed homogeneity values in the majority of the colored zones. The optical microscopy study showed different layers in the painting cross-sections. The complex polychromy was attributed to several restoration processes carried out along the time. The composition of the different layers of painting cross-sections was studied using the micro-Raman technique. The micro-Raman technique was very useful in characterizing some pigments that are difficult to determine by other experimental techniques. The study showed the presence of several pigments that had been applied in ancient and recent times.

Analytical study of Roman and Arabic wall paintings in the Patio De Banderas of Reales Alcazares' Palace using non-destructive XRD/XRF and complementary techniques

A portable XRD/XRF system and complementary laboratory techniques were employed to improve the knowledge of the procedures used to create Roman and Arabic wall paintings. Integrated physico-chemical investigations were conducted on fragments of artworks collected from the archaeological excavation of the Patio de Banderas in the Reales Alcazares' Palace of Seville (Spain), and a comparative study on the pigments from both historical periods was performed. As a result, pigments such as vermilion, red ochre, yellow ochre, green earth, Egyptian blue, carbon and phosphor-based black pigments were detected in Roman samples; however, in the Arabic fragments, only haematite was observed. In addition, the size and shape of the particles of the wall paintings were studied with an XRD 2-dimensional detector and SEM-EDX.

Solid solutions of TiB2-ZrB2 and TiB 2-HfB2 were obtained under an inert atmosphere by high-energy ball-milling mixtures of Ti/Zr/B and Ti/Hf/B, respectively. Milling promoted mechanically induced self-sustaining reactions (MSR), and the ignition time was dependent on the initial composition of the mixture. The stoichiometry of Ti1-xZrxB2 and Ti1-xHf xB2 solid solutions was controlled by adjusting the atomic ratio of the reactants. The solid solutions were characterised by X-ray diffraction, transmission electron microscopy, electron diffraction, and energy dispersive X-ray spectroscopy. The results revealed that TiB2- ZrB2 possessed a nanometric microstructure and good chemical homogeneity. However, in the TiB2-HfB2 system, an inhomogeneous solid solution was obtained when a Ti-rich mixture was employed. The solid solutions showed good thermal stability; thus, can be used as raw materials for the development of technological materials for structural applications.

Characterization of materials and conservation process of the collection of Arabic manuscript documents of granada archive histórico-provincial

This paper presents the main conclusions of our study of the Arabic documents preserved in the Archivo Histórico Provincial of Granada. The analysis of the contents of each document, the materials and inks used in their support, and also the similarities of the page layout reveals the use of identical production protocols. Furthermore, this research also enables us to establish important similarities between the paper production processes in the latter stages of the Islamic rule in the Iberian Peninsula and the earlier stages of its incorporation in the Crown of Castilla - in particular in relation to how the archival documents were issued, both externally and internally.

The high-temperature mechanical properties of the mixed ionic-electronic conductor perovskite BaCe0.95Y0.05O3−δ with average grain size of 0.40 μm have been studied in compression between 1100 and 1300 °C in air at different initial strain rates. The true stress–true strain curves display an initial stress drop, followed by an extended steady-state stage. As the temperature decreases and/or the strain rate increases, there is a transition to a damage-tolerant strain-softening stage and eventually to catastrophic failure. Analysis of mechanical and microstructural data revealed that grain boundary sliding is the primary deformation mechanism. The strength drop has been correlated with the growth of ultrafine grains during deformation, already present at grain boundaries and triple grain junctions in the as-fabricated material.

The present recommendations have been developed by the Kinetics Committee of the International Confederation for Thermal Analysis and Calorimetry (ICTAC). The recommendations offer guidance for reliable evaluation of kinetic parameters (the activation energy, the pre-exponential factor, and the reaction model) from the data obtained by means of thermal analysis methods such as thermogravimetry (TGA), differential scanning calorimetry (DSC), and differential thermal analysis (DTA). The recommendations cover the most common kinetic methods, model-free (isoconversional) as well as model-fitting. The focus is on the problems faced by various kinetic methods and on the ways how these problems can be resolved. Recommendations on making reliable kinetic predictions are also provided. The objective of these recommendations is to help a non-expert with efficiently performing analysis and interpreting its results.

In this study, the decomposition behaviour of unaltered and altered dolomitic rock samples used in Cultural Heritage buildings was studied by simultaneous TG-DTA experiments at different atmospheres, X-ray diffraction in a high-temperature chamber, and evolved gas analysis. The components of dolomite rock samples and hydrated calcium oxalate formed during the alteration processes of the rocks were characterized, and the decomposition mechanisms of these components were determined. The TG-DTA experiments carried out at CO2 atmosphere were used to determine the carbonate compounds in the rock samples. The TG-DTA study characterized the presence of organic compounds formed during the biological degradation of the rock samples, possibly responsible of the hydrated calcium oxalate formation.

Full identification of pigments used in wall paintings by Romans and Arabs that were recently discovered was achieved by the combined application of several spectroscopy methods. Identification of pigments was provided by the use of micro-Raman and FT-IR spectroscopy, while UV-Visible spectroscopy and chromatic studies permitted the authors to identify slight variations of hue attributed to mixtures of pigments. Natural earths and minerals were detected as the main pigments employed by both civilizations, although some differences were found between them. Red ochre, vermilion, yellow ochre, Egyptian blue, green earth, calcite, carbon, and possibly ivory blacks were identified in the Roman paintings. Only hematite and calcite were observed in the Arabic fragments.

This paper explores the relationship between the shapes of temperature-time curves obtained from experimental data recorded by means of constant rate thermal analysis (CRTA) and the kinetic model followed by the thermal degradation reaction. A detailed shape analysis of CRTA curves has been performed as a function of the most common kinetic models. The analysis has been validated with simulated data, and with experimental data recorded from the thermal degradation of polytetrafluoroethylene (PTFE), poly(1,4-butylene terephthalate) (PBT), polyethylene (PE) and poly(vinyl chloride) (PVC). The resulting temperature-time profiles indicate that the studied polymers decompose through phase boundary, random scission, diffusion and nucleation mechanisms respectively. The results here presented demonstrate that the strong dependence of the temperature-time profile on the reaction mechanism would allow the real kinetic model obeyed by a reaction to be discerned from a single CRTA curve.

Kinetic Analysis of Complex Solid-State Reactions. A New Deconvolution Procedure

The kinetic analysis of complex solid-state reactions that involve simultaneous overlapping processes is challenging. A method that involves the deconvolution of the individual processes from the overall differential kinetic curves obtained under linear heating rate conditions, followed by the kinetic analysis of the discrete processes using combined kinetic analysis, is proposed. Different conventional mathematical fitting functions have been tested for deconvolution, paying special attention to the shape analysis of the kinetic curves. It has been shown that many conventional mathematical curves such as the Gaussian and Lorentzian ones fit kinetic curves inaccurately and the subsequent kinetic analysis yields incorrect kinetic parameters. Alternatively, other fitting functions such as the Fraser-Suzuki one properly fit the kinetic curves independently of the kinetic model followed by the reaction and their kinetic parameters, and moreover, the subsequent kinetic analysis yields the correct kinetic parameters. The method has been tested with the kinetic analysis of complex processes, both simulated and experimental.

The plastic flow of TiCxN1-x-CoTi cermets has been investigated by uniaxial compression tests carried out in argon atmosphere at temperatures between 1100 and 1200°C. Two different cermets, with 5wt.% W or WC content as sintering additives, have been explored to assess the influence of the sintering additives on creep. The microstructural observations of deformed samples and the mechanical results indicate that the hard phase (ceramic grains) controls the plastic deformation. The stress exponent changes from 1 to 2 with increasing strain rate, suggesting a transition in the deformation mechanism from diffusional creep to grain boundary sliding; both with similar activation energy values of about 400kJ/mol. This value of activation energy agrees with C diffusion in the carbonitride grains as the strain rate controlling mechanism.

Phase transition of anatase nanoparticles into the phases TiO2-II and rutile under grinding was studied. The addition of ammonium carbamate to the reaction mixture inhibits the phase conversion and the cold welding of particles. The UV-visible absorption spectrum showed narrowing the band gap width after grinding with an ammonium carbamate additive resulting in shift of the light absorption of the ground sample towards the visible region. By EPR, intensive formation of OH• radical at irradiation of the sample with both UV (λ > 300 nm) and visible (λ > 435 nm) light was observed. High photocatalytic activity of the ground sample in visible light region was demonstrated also by measurement of kinetics of the photocatalytic decomposition of 4-chlorophenol.

In this study, we examined the annealing effect on the material obtained after acid treatment of ground vermiculite which constituted amorphous silica and β-FeOOH. The XRD patterns of the starting sample measured at temperatures from 30 to 1200°C showed that the crystalline phase was present until ~300°C; whereas the sample heated between 300 and 800°C was practically amorphous. This is in agreement with previous observations that β-FeOOH decomposes to amorphous or poorly crystalline phase, β-Fe2O3, and transforms only slowly to crystalline α-Fe2O3. At 850°C the sample showed the first signs of a crystalline phase which was fully developed at 1050°C. The XRD, HRTEM and Mössbauer spectroscopy showed, after heating at 1050°C, the presence of crystalline phase, consisting of quartz, cristobalite, α-Fe2O3 and ε-Fe2O3. This effect showed in fact that well crystallized iron oxide nanoparticles embedded into the silica matrix are usually formed at relative high temperatures (~1000°C), which is in contrast to silica-free material. Element mapping of one particle of the composite obtained by annealing the sample at the highest temperature showed well-separated Fe2O3 and SiO2 particles in a composite material. Impurities of Al and Mg (from the original vermiculite) accompanied the silica components and TiO2 associated with Fe2O3 grains was also detected.

Intercalation and dynamics of hydrated Fe2+ in the vermiculites from Santa Olalla and Ojén

Although the intercalation of Fe3+ into layered phyllosicilicates-especially into smectites-attracted much attention in the past two decades, the information about Fe2+ loaded phyllosilicates is sparse. Here we present an investigation of the Fe2+ exchanged vermiculites from Santa Olalla and Ojén (Andalusia, Spain) by means of Mössbauer spectroscopy. The room temperature Mössbauer spectra are very similar to those of the starting compounds (Na forms) except for a decrease of the contribution of structural Fe3+ and a concomitant increase of the contribution of Fe2+ sites, indicating an internal redox process. The extent of this redox reaction is different for the two vermiculites. Thus, the intercalated Fe2+ acts as an electron mediator from the external medium to the structural Fe3+ ions. A new component attributable to intercalated Fe2+ is practically invisible in the room temperature Mössbauer spectra, but increases strongly and continuously during cooling to 4.2 K, where it is the dominant feature of the Mössbauer patterns. At 4.2 K, its quadruple splitting amounts to 3.31 mm/s, which is in excellent agreement with the quadrupole slitting of Fe2+ coordinated to six water molecules in a highly symmetric octahedral arrangement. The strong decrease of the Mössbauer-Lamb factor of this component with increasing temperature indicates a weak bonding of the Fe 2+ in the interlayer space.

Forgery detection on an Arabic illuminated manuscript by micro-Raman and X-ray fluorescence spectroscopy

An Arabic manuscript, supposed to be from the 14th century, was investigated and its components (pigments and dyestuffs) characterised using micro-Raman and X-ray fluorescence (XRF) spectroscopy, the latter employing a portable XRF/X-ray diffraction (XRD) system. The presence of anatase, rutile, calcite, barite, zinc oxide, carbon black, vermilion, hematite, goethite, β-naphthol, copper phthalocyanine, pigmosol green and a brass-based pigment was detected in the different zones of the illuminated manuscript. The detection of titanium oxides, barite and organic synthetic colourants such as β-naphthol and copper phthalocyanine and derived compounds provides indisputable indication of forging, repainting or retouching after the 19th century in the image of the manuscript.

This work describes the thermal transformation of patina samples formed on the surface of dolomitic rocks used to build the Romanesque Torme's Church (Burgos, Spain). Analyses were performed using a combination of high-temperature XRD, simultaneous TG/DTA and gas mass spectrometry. The XRD analysis revealed the presence of hydrated calcium oxalates. The following three steps were proposed for the thermal transformation of the raw material: dehydration of weddellite/whewellite to form calcium oxalate, transformation of calcium oxalate to calcium carbonate, and formation of calcium oxide produced via decomposition of the calcite. DTA/TG and mass spectrometry analyses confirmed this mechanism. In addition, a high proportion of organic compounds was detected and was possibly formed via degradation of products applied for the building's conservation by the action of microorganisms attack. Mass spectrometry analysis revealed CO (and CO2) gas evolved during the transformation of CaC2O4 to CaCO3. The CO2 gas also appears at 765 °C due to the decomposition of calcium carbonate, and it appears over a large range of temperatures due to the decomposition of organic compounds. The TG analyses performed in a CO2 atmosphere were used to determine the percentages of Ca and Mg contained in dolomite, and the calcium carbonate formed by oxalate decomposition. DRIFTS and mass spectrometry results revealed the presence of several aliphatic and/or aromatic compounds containing CO groups.

Titanium-Vanadium nitride (TiVN) has been prepared from carbothermal reduction of corresponding oxides and also by direct nitridation of a mix of two metals employing the ATVC method. The characterization of the final product by X-ray diffraction, scanning electron microscopy, electron energy loss (EELS), and X-ray absorption spectroscopy (XAS) is presented. The synthesis of the ternary nitride has been possible in all range of composition and the final product is obtained with nanometric particle size and a high microhardness after sintering.

A first study of the high-temperature plasticity of ceria-doped zirconia polycrystals

Ceria zirconia ceramic alloys were sintered by high-temperature annealing, considering several synthesis temperatures to obtain a full-dense ceria zirconia ceramic material using a temperature as low as possible. It was found that fully density is achieved at temperatures of 1450 degrees C. Monolithic specimens were crept under compression at high temperatures. The creep results fitted an empirical constitutive equation consistent with a classical Ratchinger mechanism for grain switching. This result was confirmed through microstructural characterization of as-received and post-mortem specimens. Since the conventional Ashby-Verrall model is contrary to the mechanism controlling creep in other zirconia alloys, the results are considered in the framework of a new grain boundary sliding model, with particular discussion of the validity of that model for the ceria zirconia case.

The analysis of trade and their implications for understanding social interaction is a major research question of prehistoric research in Europe. Variscite is a rare mineral that offers an excellent opportunity to study trade and exchange patterns in prehistoric Europe through proveniencing of source material. In this paper we discuss the exploitation and exchange of variscite at Pico Centeno mining district during the Copper Age. XRF, XRD, and FTIR analyses of the mineral recovered at Pico Centeno mining district during archaeological survey provides a baseline mineral signature for the source and sub-sources, which were then compared to other Iberian sources and to 44 green beads from 8 megalithic tombs from two different regions, in order to test ‘provenance postulate’ and distribution models. Mineral sampled during survey at Pico Centeno mining district turned out to be pure variscite phases, while extremely varied for the studied green beads: variscite, muscovite, talc or chlorite. On testing ‘provenance postulate’ we have focused on compositional comparison of Pico Centeno’s variscite with reference from various geological sources of Western Europe. We found that the concentrations of trace elements do not allow us to establish the origin of the beads, as traditionally claimed, due to the strong natural variability on minor and trace elements of the sources. Instead we found after FTIR analysis, that different proportions of phosphate species, which results in P/Al ratios higher than 1, arose during the genesis of the variscite deposits and resulted from the associated pH and nature of the host-rocks, modifying the concentrations of PO43−, H2PO4− and HPO42−. Thus, the P/Al atomic ratio should be an indication of provenance as it is established during mineral genesis. This issue has not been addressed in any of the other studied sources where this ratio seems to be ≈1.

This paper explores the potential of sample-controlled thermal analysis (SCTA) in order to perform compositional analysis of multicomponent polymeric materials by means of thermogravimetric experiments. In SCTA experiments, the response of the sample to the temperature determines the evolution of the temperature by means of a feedback system; thus, what is controlled is not the temperature time profile, as in conventional analysis, but rather the evolution of the reaction rate with time. The higher resolving power provided by the technique has been used for determining the composition of polymer blends composed of polyvinyl chloride (PVC) and different commercial plasticizers, a system where the individual components have very similar thermal stabilities, thereby rendering useless thermogravimetric experiments run under conventional conditions. Different SCTA procedures, such as constant rate thermal analysis (CRTA), which has received special attention, and high-resolution and stepwise isothermal analysis have been tested, and the results obtained have been compared with linear heating rate technique. It has been proven that CRTA can be used to effectively determine the exact composition of the blend.

A first principles continuum analytical model for cationic segregation to the grain boundaries in complex ceramic oxides is presented. The model permits one to determine the electric charge density and the segregation-induced electric potential profiles through the grain and can be extrapolated to the range of nanostructured grain sizes. The theoretical predictions are compared with existing data for yttria-stabilized tetragonal zirconia polycrystals. The implications for physical properties (mainly high temperature plasticity and hardening behaviour) are then discussed.

Hydraulic structures of the Roman Mithraeum house in Augusta emerita, Spain

This paper deals with some of the hydraulic structures of Augusta Emerita (Merida, Spain), specifically those found in the Mithraeum House. In particular, we describe and characterise the hydraulic mortars and coatings of the viridarium water channel. The recipient of the channel was covered with two hydraulic mortars and a finishing coating. Hydrated lime was used as binder. Calcite grains with different morphology have been observed in the mortars studied. The siliceous aggregate was composed of quartz, mica and feldspars. Ceramic fragments, which were added to the mortar to improve its hydraulic properties, were composed of quartz, mica, iron oxides, anorthite and an amorphous phase; aluminium-iron silicates were used as raw materials for their manufacture. We discuss the interactions between the hydrated lime and the surface of the ceramics in the mortars.

Superplasticity in ceramics has been the subject of intense research activity for the last two decades. Quite recently, the fabrication of fully dense nanocrystalline oxides with grain size below 100 nm enabled examination of their superplastic behaviour. This work presents a critical analysis of the plasticity of two important nanostructured oxide systems: MgO and yttria tetragonal zirconia polycrystals. A thorough comparison of their plastic deformation reveals that nano-structuring may be a necessary, but not a sufficient condition for superplasticity in ceramics as commonly assumed. Instead, the changes in the chemical composition and the transport properties, through the bulk and at grain boundaries, versus temperature and grain size can induce a rich variety of mechanical responses.

In this work high purity and nanometer character titanium carbonitride TiCxN1-x powders were obtained by mechanically induced self sustaining reaction (MSR) in a high-energy planetary ball mill, from a mixture of titanium with graphite or carbon nanofiber (CNFs) in a nitrogen atmosphere. A promising method for developing these materials is the coupling of the MSR with SPS sintering technique. The product is sintered at 1400 degrees C and 1700 degrees C, obtaining a completely dense monolithic ceramic (>99% t.d). In this work, the influence of SI'S treatment and carbon precursor on material microstructures was studied and the main mechanical properties of the end material were evaluated.

Kinetic model for thermal dehydrochlorination of poly(vinyl chloride)

In this paper, a novel method for calculating degradation kinetics is presented. The method has been applied to the thermal dehydrochlorination of two different samples of PVC. It has been observed that this dehydrochlorination is complex and involves two different processes. A model that accounts for the entire dehydrochlorination is proposed. This model involves nucleation and growth and diffusion controlled mechanisms. The kinetic parameters are obtained from linear heating rate, isothermal and sample controlled thermal analysis experiments. Kinetic results obtained from the macroscopic thermal analysis measurements demonstrate the correlation between the kinetics of the thermal dehydrochlorination of PVC and the structure of this macromolecule.

Generalized Kinetic Master Plots for the Thermal Degradation of Polymers Following a Random Scission Mechanism

In this paper, the f(alpha) conversion functions for random scission mechanisms have been proposed to allow for the construction of generalized master plots suitable for these kinds of mechanisms. The master plots have been validated by their application to simulated data and to the thermal degradation of poly(butylene terephthalate), polyethylene, and poly(tetrafluoroethylene).

Mechanochemical synthesis of vanadium nitride

Vanadium nitride (VN) has been prepared by mechanosynthesis from vanadium metal under a pressurized nitrogen atmosphere in a short milling time. The characterization of the final product by X-ray diffraction, scanning electron microscopy, electron energy loss (EELS), and X-ray absorption spectroscopy (XAS) is presented. The final product, VN with 96% of purity, is obtained at room temperature with nanometric particle size and a very high microhardness after sintering. A relationship between microstructure and microhardness as well as a comparison between the VN obtained mechanical and thermal method is also presented.

Study of the Dehydroxylation-Rehydroxylation of Pyrophyllite

Pyrophyllite is a raw material of significant interest due to its large number of applications. Most of these applications require a thermal transformation of pyrophyllite; this thermal transformation implies the release of structural OH groups and the formation of new phases. In this paper, we report on the dehydroxylation of pyrophyllite and the reversibility of the process. A value of 224 +/- 16 kJ/mol for the dehydroxylation of pyrophyllite was obtained. In addition, it was observed that the partially or totally dehydroxylated pyrophyllite suffered a partial reversible rehydroxylation when cooled to room temperature. This rehydroxylation was substantiated by thermogravimetric measurements, while infrared spectroscopic studies showed that, during the rehydroxylation, the intensity of the OH band at 3675 cm-1 increased as two new bands at 3690 and 3702 cm-1 appeared. This rehydroxylation process was heavily influenced by the particle size of the pyrophyllite. Thus, smaller particles (< 1 mu m) showed a larger rehydroxylation percentage (about 12%), while the larger ones (20-40 mu m) showed a smaller percentage (about 1.6%). The extent of rehydroxylation also depended on the dehydroxylation temperature and reached a maximum value at 750 degrees C.

Mechanochemical preparation of BaTiO3-Ni nanocomposites with high dielectric constant

A mechanochemical procedure is proposed for an easy preparation of a BaTiO3-Ni composite in a single step. BaTiO3 and Ni powders available in the market are mixed by dry ball milling producing a decrease of particle size and an evenly distribution of both phases. In the sintered pellets the nickel particles are homogeneously distributed into the BaTiO3 matrix and isolated from others Ni particles. The dielectric constant of the composite is considerably higher than that of the barium titanate. Moreover, the temperature of the ferroelectric <-> paraelectric transition of the BaTiO3-Ni composite here prepared is much lower than the one of the pure BaTiO3 single phase.

The enhanced high-temperature creep resistance in alumina/single-wall carbon nanotubes (SWNTs) composites has been attributed to the unprecedented grain-boundary structure of these composites, where the SWNTs bundles segregated at the alumina grain boundaries partially impede grain-boundary sliding. In this study, the effect of SWNTs distributions at alumina grain boundaries on the creep behavior of alumina/SWNTs composites has been investigated. Microstructures of two different alumina/10 vol% SWNTs composites, one with heterogeneous and the other with homogenous distributions of SWNTs at grain boundaries, have been characterized quantitatively. The steady-state creep rate (uniaxial compression) in the heterogeneous composite has been found to be over three times higher than that in the homogeneous composite at 1300° and 1350°C (argon atmosphere). It is argued that the less uniform distribution of SWNTs at the alumina grain boundaries in the heterogeneous composite results in less effective obstruction of grain-boundary sliding, and attendant higher creep rate. This also results in more efficient recovery in that composite.

This paper describes one of the first case studies using micro-diffraction laboratory-made systems to analyse painting cross-sections. Pigments, such as lead white, vermilion, red ochre, red lac, lapis lazuli, smalt, lead tin yellow type I, massicot, ivory black, lamp black and malachite, were detected in cross-sections prepared from six Bartolome Esteban Murillo paintings by micro-Raman and micro-XRD combined with complementary techniques (optical microscopy, SEM-EDS, and FT-IR). The use of micro-XRD was necessary due to the poor results obtained with conventional XRD. In some cases, pigment identification was only possible by combining results from the different analytical techniques utilised in this study.

TiCxVy/Ni and TiCxNy/Ti-Co composites formed by ceramic and intermetallic binder phases were produced by pressureless sintering at 1400 degrees C from powders synthesized by a mechanically induced self-sustaining reaction (MSR) process. Four different composites were characterized using high-resolution electron microscopic techniques, in both scanning (SEM, HRSEM) and transmission (TEM, HRTEM, ED, EDS and EELS) modes and using an energy filtered technique (EFTEM) associated with electron energy loss spectroscopy (EELS). The microcharacterization showed that the ceramic phase with an fcc-cubic structure displayed a short-range order in many crystals detected by diffuse scattering in the ED patterns. This was possibly due to a sequence of C, N, and vacancies of both atoms along certain directions in the structure. On the other hand, even though the binder phase was introduced as metal in the reaction process, it was formed by Ni-Ti or Co-Ti known intermetallic compounds (NiTi2, Ni3Ti, and Co3Ti). An unknown Ni-Ti intermetallic structure with a Ni:Ti ratio close to 2:1 was only found in one of the synthesized composites and displayed a cubic structure with a lattice parameter, a, of about 8.7 angstrom.

Nonisothermal calorimetric study of the precipitation processes in a Cu-1Co-0.5Ti alloy

The precipitation processes in a Cu-1.0 at.%Co-0.5 at.%Ti (Cu-1.5 at.%Co2Ti) alloy were studied using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and microhardeness measurements. The analysis of the calorimetric curves from room temperature to 900 K shows the presence of two exothermic reactions attributed to the formation of CoTi and Co2Ti particles in the copper matrix. On the basis of enthalpy calculations, it was found that the decomposition begins with the precipitation of CoTi, followed by the formation of Co2Ti particles. The activation energies calculated using the modified Kissinger method were lower than the ones corresponding to diffusion of cobalt and titanium in copper. Kinetic parameters were obtained by a convolution method based on the Johnson-Mehl-Avrami (JMA) formalism. The values obtained for the parameter n were indicative of a particle nucleation process from preexistent nuclei. Microhardness measurements and TEM micrographs confirmed the formation of the mentioned phases.

A new model for the kinetic analysis of thermal degradation of polymers driven by random scission

In this paper, a series of f(alpha) kinetic equations able to describe the random scission degradation of polymers is formulated in such a way that the reaction rate of the thermal degradation of polymers that go through a random scission mechanism can be directly related to the reacted fraction. The proposed equations are validated by a study of the thermal degradation of poly(butylene terephthalate) (PBT). The combined kinetic analysis of thermal degradation curves of this polymer obtained under different thermal pathways have shown that the proposed equation fits all these curves while other conventional models used in literature do not.

On the microstructure of single wall carbon nanotubes reinforced ceramic matrix composites

A microstructural modelling of the microstructure in single wall carbon nanotubes reinforced alumina ceramics has been developed. The model accounts for the main microstructural features, being quite useful to describe the carbon nanotube distribution along the ceramic matrix. The microstructural analysis derived from this model is found to give a deeper insight into the high-temperature creep of these composites.

A complete characterisation of fibres used in Spanish artwork is necessary to provide a complete knowledge of these natural fibres and their stage of degradation. Textile samples employed as painting supports on canvas and one sample of unprocessed plant material were chosen for this study. All the samples were investigated by synchrotron radiation X-ray diffraction (SR-XRD). Flax and cotton have the Cellulose I structure. The values of the crystalline index (CI) were calculated for both types of fibres. The structure of Cellulose IV was associated with the unprocessed plant material. The information obtained by SR-XRD was confirmed by laboratory techniques including scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR).

Physical and geotechnical properties of clay phyllites

An experimental programme is presented with the aim of characterising - from physical, microstructural and geotechnical perspectives - the main properties of compacted clay phyllites. These clay phyllites are widely used as waterproofing material for roofs in the Alpujarra (Andalusia, Spain), as sealing liners in irrigation ponds, and as core material of small earthen zoned dams. An exhaustive physical-characterisation programme on the powder fraction has been followed using X-ray fluorescence (XRF), X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), chemical analysis by energy dispersive X-ray spectroscopy (EDX), thermal analysis, particle-size distribution analysis, consistency limits, and density of solid particles. From a microstructural standpoint, mercury intrusion porosimetry (MIP) tests, as well as nitrogen-adsorption tests, were carried out to characterise the pore network and surface area of the material in both natural and compacted states. The geotechnical characterisation programme on the compacted material was focused on the water-permeability and water-retention properties, the volume change on soaking (swelling or collapse), the compressibility on loading, the shear-strength properties, and the mechanical-penetration properties. In this way, an important physical and hydro-mechanical data base is provided, which could help in evaluating the suitability for using this material in a wide range of earthen constructions (liners, road subgrades, embankments, core material in zoned dams). It has been found that the material contains illite, chlorite and quartz as the main components, and feldspar, iron oxide and interstratified illite-smectite as minor ones. Despite the presence of active clay minerals, the compacted material did not display an important swelling on soaking at low stresses, as a consequence of its low specific surface and low water-retention ability. The material exhibited good compaction properties and, consequently, low water permeability plus a stiff response on loading. Nevertheless, despite the low porosity attained on the dry-side compaction, the material underwent some collapse on soaking at stresses greater than 100 kPa.

The employment of synchrotron techniques complemented by conventional laboratory systems has allowed us to deepen and improve our knowledge of Roman wall painting procedures. The palette identified in wall paintings from Pompeii and Herculaneum from the second century bc includes goethite, hematite, cinnabar, glauconite, Egyptian blue, and other components such as calcite and aragonite. Proof of the use of organic binders is provided by FTIR and PY-GC/MS. Therefore, the possibility of the use of 'a secco' techniques cannot be ruled out. Pigments in wall paintings are usually found in small percentages and conventional X-ray diffractometers do not detect them. Synchrotron radiation - high-resolution X-ray powder diffraction has allowed identification with only a few micrograms of sample.

The synthesis of solid solutions in the HfB2-ZrB2 system was conducted by mechanically induced self-sustaining reaction (MSR) processes under an inert atmosphere from elemental mixtures of Hf, Zr, and B. The stoichiometry of the Hf1-xZrxB2 solid solution phase was controlled by adjusting the Hf/Zr/B atomic ratio in the starting mixture. Composite materials with SiC were achieved by adding the required amount of SiC to the Hf/Zr/B reactant mixture. The presence of up to 20 vol% of SiC did not inhibit the MSR process. Longer milling times were required to ignite the mixture. Small amounts of the refractory phases ZrC or HfC were observed in the composite powders. The chemical composition, structure, and microstructure of products were studied by X-ray diffraction, scanning and transmission electron microscopy, electron diffraction, and energy-dispersive X-ray spectroscopy. This complete characterization confirmed the formation of P6/mmm hexagonal diboride phases with a submicrometric microstructure. The determination of the chemical composition and lattice parameters ascertained the formation of solid solutions with good chemical homogeneity in the HfB2-ZrB2 system.

High-purity, nanometer-sized titanium carbonitride powders, TiCxN1-x, were obtained with a mechanically induced self-sustaining reaction (MSR) in a high-energy planetary ball mill from a mixture of titanium and different carbon precursors under a nitrogen atmosphere. A promising method for developing dense TiCxN1-x materials is the coupling of MSR with the spark plasma sintering (SPS) technique. The powders were sintered at different temperatures to provide a completely dense monolithic ceramic (> 99% theoretical density). In this work, the influence of the carbon precursor and SPS treatment on the material microstructures were studied, and the main mechanical properties of the end material were evaluated.

A thermal study approach to roman age wall painting mortars

Roman ancient mortars have been widely studied, in connection with both diagnosis and application required for restoring. Thermoanalytical experiments performed on mortars from Pompeii and Herculaneum provided a very good understanding of the technology employed. The mortars from Pompeii were obtained by the proper mixing of lime and marble grains while mortars of Herculaneum by lime and silicates compounds. The position of the endothermic peak of calcite decomposition showed important variations in the different samples studied, which was assigned to the different crystallinity and particle sizes. Experiments under CO2 flow confirmed the presence of magnesium calcium carbonates.

Microstructural characterization of copper based alloys produced by reactive milling

The micro and nanostructure of Cu-Al, Cu-V and Cu-Ti alloys produced by reactive milling were analyzed using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Samples with different milling times (t = 0, 10, 20 and 30 h) were considered. The grain size, dislocation density and residual microstrain were evaluated form the XRD data using the Williamson-Hall and Klug-Alexander methods. The evolution of texture as a function of milling time was also studied using XRD. It was found, using TEM, that the grain size and dispersoid size were nanometric in all three alloys considered.

The Multistep Nature of the Kaolinite Dehydroxylation: Kinetics and Mechanism

The thermal dehydroxylation of kaolinite has been reexamined using small sample weights, a homogeneous particle size distribution and high-vacuum conditions in order to reduce the influences of heat and mass-transfer phenomena. The controlled rate thermal analysis (CRTA) technique, which was specially developed to minimize the pressure and temperature gradients through the sample, was employed to carry out meaningful kinetic experiments. Two advanced isoconversional methods, the Vyazovkin and the Galwey methods, were used complementarily to determine the dependence of the activation energy on the degree of conversion. For this purpose, the Vyazovkin method has been adapted to CRTA experiments. It was demonstrated that there are at least two different stages, revealing the multistep nature of this reaction. The activation energy for the first step, which is assigned to nucleation and the growth of nuclei, decreases from 100 to 75 kJ/mol. The second stage corresponds to a diffusion process and the activation energy rises to 120 kJ/mol because of the metakaolinite formation, which closes the interlamellar channels and leaves isolated patches of kaolinite from which the water escapes with difficulty.

Microscopic and spectroscopic techniques for the study of paper supports and textile used in the binding of hispano-arabic manuscripts from Al-Andalus: A transition model in the 15th century

This work focuses on the study of paper and textiles used in the binding of a series of manuscripts that share some specific characteristics that lead us to speculate on the possibility of a transitional codicological typology from the Arabic to the Christian book in Al-Andalus during the 15th century. The books we analyzed belong to the collection of the Historical Archive of Malaga, the Archive of Sacromonte Abbey, in Granada, the School of Arabic Studies and the Library of P.P. Escolapios, also in Granada. Paper physical study was performed by microscopic and spectroscopic techniques. A routine and objective method, Fourier Transform Infrared (FTIR) spectroscopy, was employed and proved to be a useful technique for the characterization of cellulosic fibres, main component of paper from the boards and the envelope flap pasteboards, and the fabric lining from the cover. The results of our research will help us to date, identify and study the evolution of the techniques, proving that the materials and innovations of the Italian paper manufacturing processes were perfectly known in the south of modern day Spain, before the Christian Reconquest.

Illuminated Arabic manuscripts have been studied, employing two laboratory-made X-ray diffraction (XRD) systems developed recently in the C2RMF laboratory. The validity of the µ-XRD and XRD portable systems for the study of this type of artworks has been demonstrated. A common observation in all the analyses is the presence of calcite and rutile; also, hematite, goethite, cinnabar, brass, anatase and barite were detected in the various colours. Differences between the results obtained by both techniques due to acquisition mode are discussed. In addition, other techniques such as X-ray fluorescence (XRF) and micro-Raman were used for the complete characterization of the manuscripts.

A comparative study of the composition and microstructure of two different brass alloys from reed pipes, one from a Spanish baroque organ and the other from a modern one, was carried out. This study allowed us to determine the procedure followed to produce the brass used to make ancient reed pipes. Moreover the distribution and correlation of lead and other trace elements present into the main component of the brass, the copper and zinc phases, of the historical tongues and shallots were established. This chemical composition was compared with that of a tongue from a twentieth-century organ. The whole study was accomplished using a combination of laboratory and synchrotron radiation techniques. X-ray fluorescence was the technique used to obtain elemental and chemical imaging of the main phases and the trace elements at a sub-micrometer scale.

Advanced combined application of μ-X-ray diffraction/μ-X-ray fluorescence with conventional techniques for the identification of pictorial materials from Baroque Andalusia paintings

The process of investigating paintings includes the identification of materials to solve technical and historical art questions, to aid in the deduction of the original appearance, and in the establishment of the chemical and physical conditions for adequate restoration and conservation. In particular, we have focused on the identification of several samples taken from six famous canvases painted by Pedro Atanasio Bocanegra, who created a very special collection depicting the life of San Ignacio, which is located in the church of San Justo y Pastor of Granada, Spain. The characterization of the inorganic and organic compounds of the textiles, preparation layers, and pictorial layers have been carried out using an XRD diffractometer, SEM observations, EDX spectrometry, FT-IR spectrometry (both in reflection and transmission mode), pyrolysis/gas chromatography/mass spectrometry and synchrotron-based μ-X-ray techniques. In this work, the advantages over conventional X-ray diffraction of using combined synchrotron-based μ-X-ray diffraction and μ-X-ray fluorescence in the identification of multi-layer paintings is demonstrated.

Characterization of sepiolite-gel-based formulations for controlled release of pesticides

Novel controlled release formulations (CRFs) were developed for reducing leaching of herbicides and contamination of groundwater. The herbicide metribuzin (MTB) was entrapped within a sepiolite-gel matrix using a novel and ultrasound-based technique. Different sepiolite/herbicide matrices (either as a gel or as a powder after freeze-drying) were prepared with pesticide loading between 28.6 and 9.1%. The release of MTB from the control released formulations into water was retarded when compared with commercial formulation (CF), except in the case of the sepiolite-gel-based formulations with lower amounts of sepiolite. The rheological properties and microstructure of these formulations were examined in detail. FTIR spectra showed that there was no evidence of herbicide inside the sepiolite tunnels. The SEM micrograph of the sepiolite-gel-based formulations showed the fibrous morphology typical of sepiolite and no separate particles of MTB were found. However, the chemical analysis by EDX confirmed the presence of S, N, and C, which were attributed to MTB, together with the fibers of sepiolite. Rheological characterization indicated that samples containing MTB develops a microstructure, which is irrespective of concentration above 1 mass % sepiolite. There was a good agreement between the microstructure characteristics and MTB release behavior.

Combined kinetic analysis of thermal degradation of polymeric materials under any thermal pathway

Combined kinetic analysis has been applied for the first time to the thermal degradation of polymeric materials. The combined kinetic analysis allows the determination of the kinetic parameters from the simultaneous analysis of a set of experimental curves recorded under any thermal schedule. The method does not make any assumptions about the kinetic model or activation energy and allows analysis even when the process does not follow one of the ideal kinetic models already proposed in the literature. In the present paper the kinetics of the thermal degradation of both polytetrafluoroethylene (PTFE) and polyethylene (PE) have been analysed. It has been concluded, without previous assumptions on the kinetic model, that the thermal degradation of PTFE obeys a first order kinetic law, while the thermal degradation of PE follows a diffusion-controlled kinetic model.

Hg/Sn amalgam degradation of ancient glass mirrors

Tin amalgam, which is obtained by pouring mercury onto a sheet of tin, has been used in the production of reflective coatings for mirrors. The corrosion processes of the amalgam layer were investigated in several mirrors from historical buildings located in southern Spain using SEM/EDS, XPS, and GID. Mercury and Sn4+ are present as spheres on the amalgam surface due to the evaporation process (∼5 nm). The profile shows a mixture of Sn2+ and Sn4+. The original amalgam was composed of a binary alloy of tin and mercury (Hg0.1Sn0.9) and metallic tin. In this paper the tin oxidation mechanism of the amalgam is described. Liquid mercury is volatile and evaporates slowly, leaving fine tin particles that oxidize easily, forming tin monoxide (SnO) and tin dioxide (SnO2). The mercury-rich phase accelerates the corrosion of the tin-rich phase.

The machinability of materials is a dynamic field with enormous implications in different industrial sectors because manufacturers are constantly looking for improvements that can increase the overall productivity. Manufacturers of cutting tool inserts need to develop products that can perform at higher speeds and last longer under increasingly rigorous operating conditions. It has been revealed that cermets may exhibit better properties and performances when solid solution of multiple hard compounds is added instead of a mixture of several binary ones. In this work, a mechanically induced self-sustaining reaction (MSR) is described as a suitable synthesis method to obtain a wide range of different new quaternary carbonitride systems by milling mixtures of elemental powders of transition metals and graphite in a nitrogen atmosphere. Characterization was carried out using X-ray powder diffraction, elemental analysis, energy dispersive X-ray analysis (EDX), scanning and transmission electron microscopy and electron diffraction (ED).

High surface area α-alumina preparation by using urban waste

A new method for preparing high surface area α-alumina from urban waste is proposed. The method consists of the precipitation of a precursor that contains bohemite mixed with a linear polymer and subsequently the thermal decomposition of the precursor by heating in nitrogen and air to 1200 °C. The resulting α-alumina consists of nanocrystals of about 100 nm aggregated into larger particles with relatively high surface area (12 m2 g−1) and a significant macropore volume of 0.545 cm3 g. Methods of X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) were used to characterize microstructure of prepared materials. Results of differential thermal analysis, thermogravimetry and emanation thermal analysis characterized the thermal behaviour of α-alumina precursors.

Kinetics of the thermal decomposition of anhydrous cobalt nitrate by SCRT method

It has been shown the ability of the Sample Controlled Reaction Temperature (SCRT) method for both discriminate the kinetic law and calculate the activation energy of the reaction. This thermal decomposition is best described by a Johnson–Mehl–Avrami kinetic model (with n = 2) with an activation energy of nuclei growth which fall in the range 52–59 kJ mol−1. The process is not a single-step because the initial rate of decomposition is likely to be limited by nucleation. The results reported here constitute the first attempt to use the new SCRT method to study the kinetic of the thermal decomposition of cobalt nitrate.

Study of the gilding technique used in polychromed stones and ceramics by dedicated laboratory-made micro X-ray diffraction and complementary techniques

This work describes the use of a new dedicated laboratory-made micro X-ray diffraction system for detecting the phases present in cross-sections of artworks. As an example, the phases present in samples from gilding ceramics and stone sculptures from the heritage of Seville (Spain) were successfully detected using this new system, which takes advantage of various devices developed for synchrotron radiation, and is complemented by the information provided by other techniques.

A recurrent error which needs to be resolved

Ortega, A
Thermochimica Acta, 491 (2009) 116-117

ABSTRACT

The recent paper by Jankovic et al. [B. Janković, B. Adnađevic, J. Jovanović; Thermochimica Acta 452 (2007) 106] and other similar papers have raised a problem which needs to be resolved. These authors use the method of Kennedy and Clark [J.A. Kennedy, S.M. Clark, Thermochimica Acta 307 (1997) 27] which is conceptually erroneous; this is analyzed in this paper.

Study of degradation processes of metals used in some artworks from the cultural heritage of Andalusia, Spain

The study of the alteration processes of metals, such as lead, bronze, iron and tin-mercury alloys, used in some of the
most important chosen artefacts of Andalusian Cultural Heritage is the main objective of this paper. Hydrocerussite
and cerussite were detected in lead seals stored in a hole of cardboard. Bronze is altered to atacamite by environmental
contamination, which is also responsible for the formation of rust from iron. Corrosion of the tin-mercury surface
of amalgam mirrors produces tin monoxide and tin dioxide and releases liquid mercury from the solid phase.

Sonication in a 1:1 mixture (volume ratio) of water and concentrated H2O2 (30%) is a soft method for particle size reduction of phyllosilicate minerals like vermiculites. Repeated sonication causes a particle size reduction to about 70 nm for the Santa Olalla and to 45 nm for the Ojén-vermiculite. In this context the question arises whether the strong oxidising effect of the hydrogen peroxide affects the oxidation state of the iron in the vermiculites. Therefore, the Fe3+/Fetotal ratio before and after sonication was determined by means of Mössbauer spectroscopy. Whereas this ratio was found to remain almost constant in the Santa Olalla vermiculite, it increased from 0.79 to 0.85 in case of the Ojén sample. In the latter case, the oxidation is accompanied by a decrease of the layer charge.

Surprisingly, sonication in pure water leads to a decrease of the Fe3+/Fetotal ratio in the case of the Ojén-vermiculite, i.e., to an increase of the Fe2+ fraction to roughly twice the value before sonication. Again the Fe3+/Fetotal ratio of the Santa Olalla vermiculite remains unchanged. The surface area SBET of the reduced Ojén-vermiculite amounts to 50 m2/g, which is close to the value obtained in the presence of hydrogen peroxide. The results presented should be taken as a warning that particle size reduction by sonication may be accompanied by a change of the redox state and the layer charge of the material.

Study of ground and unground leached vermiculite

Grinding of clays modifies their surfaces and can significantly affect their leaching behaviour. The acid reaction of vermiculite from Santa Olalla (Huelva, Spain) with HCl at various concentrations was affected by grinding and acid concentration. The acid leaching of ground vermiculite for 3 min with 1 M HCl solution at 80 °C for 24 h removed MgO and Al2O3 almost completely, leaving a residue containing SiO2 and Fe2O3. X-ray diffraction analysis showed the presence of akaganeite (β-FeOOH) and an amorphous phase (silica). Porosity studies showed a very high specific surface area for ground samples compared with unground vermiculite samples, attributed to the presence of iron in the residue coming from structural iron. High resolution transmission electron microscopy (HRTEM) confirmed the presence of iron oxyhydroxides embedded in the silica material. The particle morphology of the iron oxides corresponded well to akaganeite microcrystals precipitated from solution. The leached vermiculite residue also contained Cl− and a small amount of Ti4+, which were accumulated into the akaganeite microcrystals.

The properties of TiCxN1−x/(Ni or Co) cermets sintered by a pressureless method from powder mixtures, and obtained for the first time by a mechanically induced self-sustaining reaction process (MSR), were studied. The hardness, toughness, friction and wear coefficients, and oxidation resistance were determined. It was shown that cermets obtained from powdered materials synthesized in one single MSR step possessed improved mechanical properties, similar to those obtained in cermets with more complex bulk compositions. Higher wear resistances were observed in cermets whose hard phase was richer in carbon. The oxidation resistance of the cermets depended primarily on the binder composition. This resistance was better for those cermets with cobalt as the binder. Superior oxidation resistance was displayed when small amounts of W or Mo were incorporated into the binder.

Comparison between micro-Raman and micro-FTIR spectroscopy techniques for the characterization of pigments from Southern Spain Cultural Heritage

An extensive overview of the complementary use of micro-FTIR and micro-Raman spectroscopy in the Cultural Heritage studies is described in this work.

The samples have been prepared using the cross-section technique. This technique allows the examination of a large portion of a single paint layer in its original condition. A variety of pigments from samples belonging principally to the Cultural Heritage of Southern Spain were characterized by micro-Raman spectroscopy using visible excitation sources and micro-FTIR spectroscopy. The pigments studied comprise blue (azurite, ultramarine blue, Prussian blue), red (vermilion, haematite, red ochre, red lead, etc.), ochre and yellow (goethite, orpiment, realgar, etc.), green (malachite, copper resinate), and white (calcite, gypsum, white lead, titanium white, barite, lithopone) pigments, among others. An orientation is given for their appropriate and unequivocal characterization. Characterization by micro-FTIR and micro-Raman presents difficulties with some pigments. In these cases, analysis by EDX solves most of these doubts. The combined use of both spectroscopic techniques, together with SEM–EDX microanalysis, provides one of the most useful methods in the characterization (and possible dating) of materials used in Cultural Heritage.

Study by grazing incident diffraction and surface spectroscopy of amalgams from ancient mirrors

Characterization of four amalgam surfaces, with different alteration degrees from Andalusia historical mirrors, has been carried out by grazing-incidence X-ray diffraction (GIXRD), and other spectroscopic techniques (SEM/EDX, XPS, and REELS). The combination of all these techniques allows determining the corrosion state of the amalgams. The results show that the amalgams are composed in all cases of a binary alloy of tin and mercury. As mercury has high vapour pressure at RT, it slowly segregates and eventually evaporates, it leaves finely divided particles of tin that easily can be oxidize, forming tin monoxide (SnO) and tin dioxide (SnO2). In one of the samples, most of the amalgam remains unoxidized, since Hg0.1Sn0.9 and metallic Sn phases are the major components; in two other samples, Hg0.1Sn0.9 and Sn phases are not detected while SnO2 and SnO phases appear. Finally, in the last studied sample, only SnO2 phase is detected. The surface analyses of these samples by XPS show that, for most of them an unique chemical species (Sn4+) is found.

General Quantum-Mechanical Study on the Hydrolysis Equilibria for a Tetravalent Aquaion: The Extreme Case of the Po(IV) in Water

A systematic study of the different hydrolyzed species derived from the hydrated Po(IV) in water, [Po(H2O)n(OH)m](4−m) for 1 m 4, and 4 m + n 9, has been carried out by means of quantum mechanical computations. The effects of outer solvation shells have been included using a polarizable continuum dielectric model. For a fixed number of hydroxyl groups, the preferred hydration number for the Po(IV) can be determined in terms of Gibbs energy. It is shown that the hydration number (n) systematically decreases with the increase in the number of hydroxyl groups (m) in such a way the total coordination number (n + m) becomes smaller, being 9 in the aquocomplex and 4 in the neutral hydroxo-complex. Free energies for the hydrolysis processes involving Po(IV) complexes and a different number of hydroxyl groups have been computed, revealing the strong tendency toward hydrolysis exhibited by these complexes. The predominant species of Po(IV) in aqueous solutions are ruled by a dynamical equilibrium involving aggregates containing in the first coordination shell OH− groups and water molecules. Although there is not experimental information to check the theoretical predictions, theoretical computations in solution seem to suggest that the most likely clusters are [Po(H2O)5(OH)2]2+ and [Po(H2O)4(OH)2]2+. The geometry of the different clusters is ruled by the trend of hydroxyl groups to be mutually orthogonal and to promote a strong perturbation of the water molecule in trans-position by lengthening the Po−H2O distances and tilting the corresponding bond angle. A general thermodynamic cycle is defined to compute the Gibbs free energy associated to the formation of the different hydrolyzed forms in solution. From it, the estimates of pKa values associated to the different protolytic equilibria are provided and discussed. Comparison of the relative values of pKa along a hydrolysis series with the experimental values for other tetravalent cations supports its consistency.